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5/8: This is one epidemiologist's analysis of several "superexposure" events, as well as the math required for infection. Recommended by bona-fide scientist, Katie Mattaini!

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5/8: This is one epidemiologist's analysis of several "superexposure" events, as well as the math required for infection. Recommended by bona-fide scientist, Katie Mattaini!

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It seems many people are breathing some relief, and I'm not sure why. An epidemic curve has a relatively predictable upslope and once the peak is reached, the back slope is also predictable. Assuming we have just crested in deaths at 70k, that would mean that if we stay locked down, we lose another 70,000 people over the next 6 weeks as we come off that peak. That's what's going to happen with a lockdown.

As states reopen, and we give the virus more fuel, all bets are off. I understand the reasons for reopening the economy, but I've said before, if you don't solve the biology, the economy won't recover.

There are very few states that have demonstrated a sustained decline in numbers of new infections. Indeed, the majority are still increasing and reopening. As a simple example of the USA trend, when you take out the data from New York and just look at the rest of the USA, daily case numbers are increasing. Bottom line: the only reason the total USA new case numbers look flat right now is because the New York City epidemic was so large and now it is being contained.

So throughout most of the country we are going to add fuel to the viral fire by reopening. It's going to happen if I like it or not, so my goal here is to try to guide you away from situations of high risk.

Where are people getting sick?

We know most people get infected in their own home. A household member contracts the virus in the community and brings it into the house where sustained contact between household members leads to infection.

But where are people contracting the infection in the community? I regularly hear people worrying about grocery stores, bike rides, inconsiderate runners who are not wearing masks.... are these places of concern? Well, not really. Let me explain.

In order to get infected you need to get exposed to an infectious dose of the virus; the estimate is that you need about ~1000 SARS-CoV2 viral particles for an infection to take hold, but this still needs to be determined experimentally. That could be 1000 viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths. Each of these situations can lead to an infection.

How much Virus is released into the environment?

A Toilet flush: Without a seat to close, a single flush releases ~8000 droplets into the air. If the person using the restroom before you was infected, you have a chance of contracting the virus via breathing the air in the bathroom. While the paper in question did not look for live virus, it is clear that infected people are releasing, at a minimum, viral RNA, in bowel movements. Until further experiments are done to determine whether is is just viral fragments, or infectious material, I would avoid public bathrooms or wait a few minutes before entering so gravity can bring the droplets to the floor.

A Cough: A single cough releases about 3,000 droplets and droplets travels at 50 miles per hour. Most droplets are large, and fall quickly (gravity), but many do stay in the air and can travel across a room in a few seconds.

: A single sneeze releases about 30,000 droplets, with droplets traveling at up to 200 miles per hour. Most droplets are small and travel great distances (easily across a room).

If a person is infected, the droplets in a single cough or sneeze may contain as many as 200,000,000 (two hundred million) virus particles which can all be dispersed into the environment around them.

A breath: A single breath releases 50 - 5000 droplets. Most of these droplets are low velocity and fall to the ground quickly. There are even fewer droplets released through nose-breathing. Importantly, due to the lack of exhalation force with a breath, viral particles from the lower respiratory areas are not expelled.

Unlike sneezing and coughing which release huge amounts of viral material, the respiratory droplets released from breathing only contain low levels of virus. We don't have a number for SARS-CoV2 yet, but we can use influenza as a guide. We know that a person infected with influenza releases about 3 - 20 virus RNA copies per minute of breathing

Remember the formulae: Successful Infection = Exposure to Virus x Time

If a person coughs or sneezes, those 200,000,000 viral particles go everywhere. Some virus hangs in the air, some falls into surfaces, most falls to the ground. So if you are face-to-face with a person, having a conversation, and that person sneezes or coughs straight at you, it's pretty easy to see how it is possible to inhale 1,000 virus particles and become infected.

But even if that cough or sneeze was not directed at you, some infected droplets--the smallest of small--can hang in the air for a few minutes, filling every corner of a modest sized room with infectious viral particles. All you have to do is enter that room within a few minutes of the cough/sneeze and take a few breaths and you have potentially received enough virus to establish an infection.

But with general breathing, 20 copies per minute into the environment, even if every virus ended up in your lungs, you would need 1000 copies divided by 20 copies per minute = 50 minutes.

increases the release of respiratory droplets about 10 fold; ~200 copies of virus per minute. Again, assuming every virus is inhaled, it would take ~5 minutes of speaking face-to-face to receive the required dose.

The exposure to virus x time formulae is the basis of contact tracing. Anyone you spend greater than 10 minutes with in a face-to-face situation is potentially infected. Anyone who shares a space with you (say an office) for an extended period is potentially infected. This is also why it is critical for people who are symptomatic to stay home. Your sneezes and your coughs expel so much virus that you can infect a whole room of people.

What is the role of asymptomatic people in spreading the virus?

Symptomatic people are not the only way the virus is shed. We know that at least 44% of all infections--and the majority of community-acquired transmissions--occur from people without any symptoms (asymptomatic or pre-symptomatic people). You can be shedding the virus into the environment for up to 5 days before symptoms begin.

Infectious people come in all ages, and they all shed different amounts of virus. The figure below shows that no matter your age (x-axis), you can have a little bit of virus or a lot of virus (y-axis). ()

The amount of virus released from an infected person changes over the course of infection and it is also different from person-to-person. Viral load generally builds up to the point where the person becomes symptomatic. So just prior to symptoms showing, you are releasing the most virus into the environment. Interestingly, the data shows that just 20% of infected people are responsible for releasing 99% of all the virus into the environment. ( )

So now let's get to the crux of it. Where are the personal dangers from reopening?

When you think of outbreak clusters, what are the big ones that come to mind? Most people would go to the cruise ships. But you would be wrong. Ship outbreaks don't even land in the top 50 outbreaks to date.

The biggest outbreaks are in prisons, religious ceremonies, and workplaces, such a meat packing facilities and call centers. Any environment that is enclosed, with poor air circulation and high density of people, spells trouble.

The biggest super-spreading events are:

Meat packing: In meat processing plants, densely packed workers must communicate to one another amidst the deafening drum of industrial machinery and a cold-room virus-preserving environment. There are now outbreaks in 115 facilities across 23 states, 5000+ workers infected, with 20 dead. ()

Weddings, funerals, birthdays: 10% of early spreading events

Business networking: Face-to-face business networking like the Biogen Conference in Boston in March. Or the businessman from Maine who spread the disease to Malaysia while on a business trip.

As we move back to work, or go to a restaurant, let's look at what can happen in those environments.

Restaurants: Some really great shoe-leather epidemiology demonstrated clearly the effect of a single asymptomatic carrier in a restaurant environment (see below). The infected person (A1) sat at a table and had dinner with 9 friends. Dinner took about 1 to 1.5 hours. During this meal, the asymptomatic carrier released low-levels of virus into the air from their breathing. Airflow (from the restaurant's various airflow vents) was from right to left. Approximately 50% of the people at the infected person's table became sick over the next 7 days. 75% of the people on the adjacent downwind table became infected. And even 2 of the 7 people on the upwind table were infected (believed to happen by turbulent airflow). No one at tables E or F became infected, they were out of the main airflow from the air conditioner on the right to the exhaust fan on the left of the room. ()

Workplaces: Another great example is the outbreak in a call center (see below). A single infected employee came to work on the 11th floor of a building. That floor had 216 employees. Over the period of a week, 94 of those people become infected (43.5%: the blue chairs). 92 of those 94 people became sick (only 2 remained asymptomatic). Notice how one side of the office is primarily infected, while there are very few people infected on the other side. Being in an enclosed space, sharing the same air for a prolonged period increases your chances of exposure and infection. The estimates were that 94% of infections were from respiratory droplets / respiratory exposure, and roughly 6% from fomite transfer (door handles, shared water coolers, elevator buttons etc). Another 3 people on other floors of the building were infected, most likely from fomite transfer (doors handles, elevator buttons etc) or from being in an enclosed elevator with the infected person. ()

Choir: The church choir in Washington State. Even though people were aware of the virus and took steps to minimize transfer; e.g. they avoided the usual handshakes and hugs hello, people also brought their own music to avoid sharing, and socially distanced themselves during practice. A single asymptomatic carrier infected most of the people in attendance. The choir sang for 2 1/2 hours, inside an enclosed church which was roughly the size of a volleyball court.

Singing, to a greater degree than talking, aerosolizes respiratory droplets extraordinarily well. Deep-breathing while singing facilitated those respiratory droplets getting deep into the lungs. Two and half hours of exposure ensured that people were exposed to enough virus over a long enough period of time for infection to take place. Over a period of 4 days, 45 of the 60 choir members developed symptoms, 2 died. The youngest infected was 31, but they averaged 67 years old.)

Indoor sports: While this may be uniquely Canadian, a super spreading event occurred during a curling event in Canada. A curling event with 72 attendees became another hotspot for transmission. Curling brings contestants and teammates in close contact in a cool indoor environment, with heavy breathing for an extended period. This tournament resulted in 24 of the 72 people becoming infected. ()

Birthday parties / funerals: Just to see how simple infection-chains can be, this is a real story from Chicago. The name is fake. Bob was infected but didn't know. Bob shared a takeout meal, served from common serving dishes, with 2 family members. The dinner lasted 3 hours. The next day, Bob attended a funeral, hugging family members and others in attendance to express condolences. Within 4 days, both family members who shared the meal are sick. A third family member, who hugged Bob at the funeral became sick. But Bob wasn't done. Bob attended a birthday party with 9 other people. They hugged and shared food at the 3 hour party. Seven of those people became ill. Over the next few days Bob became sick, he was hospitalized, ventilated, and died.

But Bob's legacy lived on. Three of the people Bob infected at the birthday went to church, where they sang, passed the tithing dish etc. Members of that church became sick. In all, Bob was directly responsible for infecting 16 people between the ages of 5 and 86. Three of those 16 died.

The spread of the virus within the household and back out into the community through funerals, birthdays, and church gatherings is believed to be responsible for the broader transmission of COVID-19 in Chicago. ()

Sobering right?

Commonality of outbreaks

The reason to highlight these different outbreaks is to show you the commonality of outbreaks of COVID-19. All these infection events were indoors, with people closely-spaced, with lots of talking, singing, or yelling. The main sources for infection are home, workplace, public transport, social gatherings, and restaurants. This accounts for 90% of all transmission events. In contrast, infections while shopping appear to be responsible for 3-5% of infections. ()

Importantly, of the countries performing contact tracing properly, only a single outbreak has been reported from an outdoor environment (less than 0.3% of traced infections). ()

So back to the original thought of my post.

Indoor spaces, with limited air exchange or recycled air and lots of people, are concerning from a transmission standpoint. We know that 60 people in a volleyball court-sized room (choir) results in massive infections. Same situation with the restaurant and the call center. Social distancing guidelines don't hold in indoor spaces where you spend a lot of time, as people on the opposite side of the room were infected.

The principle is viral exposure over an extended period of time. In all these cases, people were exposed to the virus in the air for a prolonged period (hours). Even if they were 50 feet away (choir or call center), even a low dose of the virus in the air reaching them, over a sustained period, was enough to cause infection and in some cases, death.

Social distancing rules are really to protect you with brief exposures or outdoor exposures. In these situations there is not enough time to achieve the infectious viral load when you are standing 6 feet apart or where wind and the infinite outdoor space for viral dilution reduces viral load. The effects of sunlight, heat, and humidity on viral survival, all serve to minimize the risk to everyone when outside.

When assessing the risk of infection (via respiration) at the grocery store or mall, you need to consider the volume of the air space (very large), the number of people (restricted), how long people are spending in the store (workers - all day; customers - an hour). Taken together, for a person shopping: the low density, high air volume of the store, along with the restricted time you spend in the store, means that the opportunity to receive an infectious dose is low. But, for the store worker, the extended time they spend in the store provides a greater opportunity to receive the infectious dose and therefore the job becomes more risky.

Basically, as the work closures are loosened, and we start to venture out more, possibly even resuming in-office activities, you need to look at your environment and make judgments. How many people are here, how much airflow is there around me, and how long will I be in this environment. If you are in an open floorplan office, you really need critically assess the risk (volume, people, and airflow). If you are in a job that requires face-to-face talking or even worse, yelling, you need to assess the risk.

If you are sitting in a well ventilated space, with few people, the risk is low.

If I am outside, and I walk past someone, remember it is "dose and time" needed for infection. You would have to be in their airstream for 5+ minutes for a chance of infection. While joggers may be releasing more virus due to deep breathing, remember the exposure time is also less due to their speed.

While I have focused on respiratory exposure here, please don't forget surfaces. Those infected respiratory droplets land somewhere. Wash your hands often and stop touching your face!

As we are allowed to move around our communities more freely and be in contact with more people in more places more regularly, the risks to ourselves and our family are significant. Even if you are gung-ho for reopening and resuming business as usual, do your part and wear a mask to reduce what you release into the environment. It will help everyone, including your own business.
Erin S. Bromage, Ph.D Dr. Bromage's research focuses on the evolution of the immune system, the immunological mechanisms responsible for protection from infectious disease, and the design and use of vaccines to control infectious disease in animals. He also focuses on designing diagnostic tools to detect biological and chemical threats in the environment in real-time. ., is an Associate Professor of Biology at the University of Massachusetts Dartmouth. Dr. Bromage graduated from the School of Veterinary and Biomedical Sciences James Cook University, Australia where his research focused on the epidemiology of, and immunity to, infectious disease in animals. His Post-Doctoral training was at the College of William and Mary, Virginia Institute of Marine Science in the Comparative Immunology Laboratory of late Dr. Stephen Kaattari.
Dr. Bromage joined the Faculty of the University of Massachusetts Dartmouth in 2007 where he teaches courses in Immunology and Infectious disease, including a course this semester on the Ecology of Infectious Disease which focused on the emerging SARS-CoV2 outbreak in China.

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It seems many people are breathing some relief, and I'm not sure why. An epidemic curve has a relatively predictable upslope and once the peak is reached, the back slope is also predictable.

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5/4: NOT A REAL STUDY! Science journals and scientists from here on out . . .
https://www.vice.com/en_us/article/v74az9/the-viral-study-about-runners-spreading-coronavirus-is-not-actually-a-study

Slipstreams and Exercise (I had been wondering about this re: Wissahickon)

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What is a safe distance when running, biking and walking during COVID-19 times? It is further than the typical 1-2 meter as prescribed in different countries!
In a lot of countries walking, biking and jogging are welcome activities in these times of COVID-19. However, it is important to note that you need to avoid each other's slipstream when doing these activities. This comes out of the result of a study by the KU Leuven (Belgium) and TU Eindhoven (Netherlands).

The typical social distancing rule which many countries apply between 1-2 meters seems effective when you are standing still inside or even outside with low wind. But when you go for a walk, run or bike ride you better be more careful. When someone during a run breathes, sneezes or coughs, those particles stay behind in the air. The person running behind you in the so-called slip-stream goes through this cloud of droplets.

The researchers came to this conclusion by simulating the occurrence of saliva particles of persons during movement (walking and running) and this from different positions (next to each other, diagonally behind each other and directly behind each other). Normally this type of modelling is used to improve the performance level of athletes as staying in each other air-stream is very effective. But when looking at COVID-19 the recommendation is to stay out of the slipstream according to the research.

The results of the test are made visible in a number of animations and visuals. The cloud of droplets left behind by a person is clearly visible. "People who sneeze or cough spread droplets with a bigger force, but also people who just breathe will leave particles behind". The red dots on the image represent the biggest particles. These create the highest chance of contamination but also fall down faster. "But when running through that cloud they still can land on your clothing" according to Professor Bert Blocken.

Out of the simulations, it appears that social distancing plays less of a role for 2 people in a low wind environment when running/walking next to each other. The droplets land behind the duo. When you are positioned diagonally behind each other the risk is also smaller to catch the droplets of the lead runner. The risk of contamination is the biggest when people are just behind each other, in each other's slipstream.

On the basis of these results the scientist advises that for walking the distance of people moving in the same direction in 1 line should be at least 4-5 meter, for running and slow biking it should be 10 meters and for hard biking at least 20 meters. Also, when passing someone it is advised to already be in different lane at a considerable distance e.g. 20 meters for biking.

This is definitely information I will be taking into account and it also puts in perspective the closing of busy parks etc. Perhaps the better way is just running in the street, on your own or at least with sufficient distance. Stay safe...

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Belgian-Dutch Study: Why in times of COVID-19 you can not walk/run/bike close to each other.

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What is a safe distance when running, biking and walking during COVID-19 times? It is further than the typical 1-2 meter as prescribed in different countries! In a lot of countries walking, biking and jogging are welcome activities in these times of COVID-19.

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Layout of 4 Possible Timelines (useful reality check)

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The coronavirus outbreak may last for a year or two, but some elements of pre-pandemic life will likely be won back in the meantime.

Maria Litwa / Laif / Redux

Editor's Note: The Atlantic is making vital coverage of the coronavirus available to all readers. Find the collection here.

Updated at 4:40 ET on March 30, 2020.
The new coronavirus has brought American life to a near standstill, closing businesses, canceling large gatherings, and keeping people at home. All of those people must surely be wondering: When will things return to normal?

The answer is simple, if not exactly satisfying: when enough of the population-possibly 60 or 80 percent of people-is resistant to COVID-19 to stifle the disease's spread from person to person. That is the end goal, although no one knows exactly how long it will take to get there.

There are two realistic paths to achieving this "population-level immunity." One is the development of a vaccine. The other is for the disease to work its way through the population, surely killing many, but also leaving many others-those who contract the disease and then recover-immune. "They're just Teflon at that point," meaning they can't get infected again and they won't pass on the disease, explains Andrew Noymer, a public-health professor at UC Irvine. Once enough people reach Teflon status-though we don't yet know if recovering from the disease confers any immunity at all, let alone lifelong immunity-normalcy will be restored. (It may also turn out to be the case that people who are immune to the disease can still pass it on under certain circumstances.)*

Unfortunately, both of these paths could be a year or two long, but degrees of normalcy will likely be won back in the meantime: Come summer, Americans might get restaurants but no music festivals, offices but no crowded beaches, bars with spaced-out seating. Projecting when each facet of daily life will be restored would be easier if public-health authorities had an omniscient view of who is infected, who has recovered and become immune, and who is still susceptible-this is the information that would emerge from widespread testing, which the United States is terribly behind on deploying.
Read: The crisis could last 18 months. Be prepared.
As such, America is currently left with self-isolation, a blunt tactic that can slow the spread of the virus, potentially sparing the country's hospitals from a catastrophic overload of patients, but that comes at the cost of freezing daily life. Epidemiologists I interviewed stressed that they have no idea when life will be unfrozen, but they walked me through a series of possible timelines on which Americans might be able to safely start leaving the house to make money or do fun things again. Below are those timelines, including some turning points to look out for in the coming weeks, months, and years.

No matter what, staying safe means staying home for a while yet, despite Donald Trump's desire, expressed a t a Fox News town hall on Tuesday, "to have the country opened up, and just raring to go, by Easter." Moving back toward normalcy at this early stage could be disastrous. "Prematurely ending severe social distancing would be an incredible blunder that would have major human consequences," Noymer told me. "What is 'prematurely'? The truth is, we don't know yet, exactly, but it's longer than a fortnight. It could be eight to 12 weeks."

TIMELINE ONE: ONE TO TWO MONTHS

I should note that the experts I spoke with think this timeline is highly unlikely. But America could be through with most of its social distancing in a month or two if the coronavirus turns out "to not be a serious pathogen, suddenly," said William Hanage, an epidemiology professor at the Harvard T. H. Chan School of Public Health. "All of the people who are now infected, instead of behaving like the infected people we've seen [before], have very mild disease, and we realize that immunity is being generated." This "false alarm" outcome would of course be fantastic, but also produce "a lot of head-scratching" among public-health experts, Hanage said.

Another path to a short-term resolution is much grimmer: Too-lax social distancing could produce what Noymer calls a "big, short, sharp shock" of infections sometime in the next few months, overwhelming the health-care system and killing enormous numbers of people. After such a catastrophe, it's conceivable that lots of people infected with the virus would recover, bringing the broader population closer, if not all the way, to immunity.

Both of these eventualities would make it okay to go out again in a couple of months, but even if Americans are still mostly cooped up at home in late spring, public-health experts will have learned more about the virus by then. Perhaps most important, they should know how much strain this first wave of infections will have put on America's hospitals, and thus how effective containment efforts have been. This information isn't readily available now, Hanage explained, because people who get infected today generally won't require intensive care until several weeks from now. Also in a month or two, public-health authorities and researchers will likely have a better sense of whether those who recover from an infection are immune to future infections, and if so, for how long. That information will come in handy for containment efforts.
Read: How the pandemic will end
TIMELINE TWO: THREE TO FOUR MONTHS

In this timeline, Hanage speculated, "we learn some things about the virus that make us much more confident about being able to resume various activities. One of them might be that we actually have substantial immunity already, through mild infections" or even asymptomatic ones.

These are the sorts of things that could be learned from months of testing both people who have symptoms and people who don't. Two types of tests matter here: one that detects the presence of the virus itself, and one that detects the antibodies that people develop when they're immune to it.

With this new information, Hanage said, it might be possible to isolate contagious or more vulnerable people, while a large portion of the population returns to something resembling normal life. "You can have fewer tables to a restaurant, for instance, or a smaller number of people at a bar," he said. Meanwhile, if some places have much higher incidences of the disease than others, people in some states and cities might leave home sooner or during different periods than people elsewhere in the country.

Michael Stoto, a professor of health-systems administration and population health at Georgetown University, told me that three variables dictate the spread of a disease: "how many people the average person encounters in a day when transmission could take place" (whether through face-to-face interaction or from touching the same surface), "the chance that the virus will be transmitted in each of those interactions," and "the proportion of people that you encounter who are themselves infected."

If more and better-targeted testing started to yield a fuller picture of the spread of the virus, Stoto said, public-health authorities might choose to focus on one variable more than another. For instance, if testing data indicated that reducing people's number of encounters (the first variable) would be highly effective, maybe restaurants and small businesses would reopen, but large, crowded events would be canceled or remain postponed. "Some of the extreme things we're doing now, we might be able to drop sooner rather than later," he said.

And in three to four months, researchers might have identified a treatment for COVID-19-not a cure, but something that could quickly and reliably ease symptoms and prevent deaths. This wouldn't eliminate the continued need for social distancing, since large-scale outbreaks would still be possible, but it could reduce the risk of overburdening the country's hospitals if an outbreak arose.

To Hanage, this timeline is likelier than the false-alarm scenario, but "all of this is Who knows exactly? "
Read: The president is trapped
TIMELINE THREE: FOUR TO 12 MONTHS

One big unresolved question about COVID-19 is whether, like the flu, its spread will slow substantially during the summer. Researchers have a few theories for why summer is a season unfriendly to the flu-it could be that higher temperatures and increased UV radiation are inhospitable to some viruses, and/or that most schools are out of session, depriving viruses of a crucial breeding ground. But whether either of those theories applies to the coronavirus is not yet known.

Noymer guesses that we'll find out if COVID-19 is seasonal sometime in the next two to three months, and here is where Timeline Three splits in two: In one possible universe, the virus recedes in the summer. In the other, it doesn't. In both, at least some of the social distancing measures now in place continue into the second half of the year.

In the first universe, Noymer said, summer will be a bit more fun than spring was, at least in the Northern Hemisphere. Outdoor activities in small groups would probably be fine. Maybe bars and restaurants would reopen. But large gatherings would likely be out: "No Lollapalooza, no Major League Baseball, no crowded beaches," Noymer guesses.

Hanage thinks that sports leagues might resume in the summer but without crowds, and that TV shows might forgo studio audiences. Meanwhile, stores might cap the number of shoppers allowed in at once. "I really don't think that large crowds are going to be a thing for quite some time," he said. But the smaller-scale units of American life might be phased back in.

It might even be (relatively) safe to travel to see loved ones. "Once it's everywhere, and you are as likely to get infected in your local convenience store as anywhere, travel restrictions make very little sense," Hanage said. "That said, there would need to be some responsible measures to help people not get too crowded in the airports."

The downside of this closer-to-normal summer is that a resurgence of the disease in six months or so is a strong possibility (though not guaranteed). This "fall wave" of infections might arrive in September or October, reintroducing the need for social distancing. That social distancing might be on par with what's happening now, or it might be eased a bit: By then, many people could have developed immunity, and could theoretically go out without risking infection. And we'll know more about the virus too. If we've learned by the fall that children don't spread it, schools might even reopen.

Also, the country would hopefully be in a better position to absorb another wave of infections. The summer would be a good time to produce more ventilators, hospital beds, and the protective equipment that health-care workers wear to prevent infection. "If we get seasonality, saving our bacon in the short term ... we need to use the summer lull to steel our response" in the fall, Noymer said. With the proper steeling, social distancing might be able to be scaled back further.

In the second possible universe, we don't get a summer reprieve. The current oncoming spike in cases would, hopefully, subside as a result of isolation measures taken now, but the risk of a resurgence would remain high in the warmer months. If the number of cases isn't falling significantly by early to mid-June, Noymer said, that's how we'd probably know the virus isn't seasonal.

At that point, social-distancing measures could be modified according to the situation. If another onslaught of infections appears to be approaching, Americans could be stuck where they are now. But if there's good enough data indicating that hospitals shouldn't be overwhelmed, social distancing could be scaled back.
Read: What could happen if the coronavirus closed schools for days, weeks, or even months
"Once the [current] wave is dealt with, then some things might relax-a little," Hanage said. More out-of-the-house working and socializing might take place, but this would still be a world with rigorous hand-washing, well-smothered sneezing, and generous amounts of hand sanitizer (and suspicion of anyone who disregards these public-health norms). In all likelihood, people who can work remotely or order food via delivery would still do so instead of leaving the house.

The fall could introduce some chaos, regardless of the virus's seasonality. "There's the small matter of an election, which is a potentially huge superspreading event," Hanage noted. (He also worries that social-media rumors of, say, people coughing near a certain polling place could cause turnout there to plummet.) And of course, the flu will return around the time of the election too, making it hard to tell, without a test, if any given person has COVID-19 or the flu-an ambiguity that isn't as onerous now, during the tail end of flu season. The election and the flu are reminders that all of the things that happen under normal circumstances-including natural disasters (summer and fall are hurricane and wildfire season too, don't forget)-won't necessarily be put on hold during this highly abnormal time.

TIMELINE FOUR: 12 TO 18 MONTHS (OR LONGER)

Amid everything I've described so far-the crowd-free baseball games, the bars and restaurants with spaced-out seating, and so on-researchers around the world will have been scrambling to develop a vaccine. Spring 2021 is about the earliest anyone expects one to be available. "Anything faster would be world-record, lightning speed," Noymer said. If it's a "rough draft and needs to be polished," it would take longer, possibly another six months or a year after next spring.

Vaccines take so long to make because they are difficult to perfect. There are a series of methodical trials done to make sure they don't harm healthy people, to make sure they generate the desired antibodies, and to make sure those antibodies actually defend against the disease. These aren't overcautious bureaucratic safeguards; if researchers are making something that's going to be pumped into the arms of hundreds of millions, probably billions, of people, they want to make sure it's just right.

And if it's just right, normal life will resume, but not immediately. "The logistics of vaccinating [nearly] 350 million people is no mean feat," Stoto said. He also noted that, "assuming that it doesn't all arrive in one big batch," some sort of system would need to be in place for determining who gets the first doses: the people most vulnerable to the disease? Health-care workers?

It's also possible that no one is able to develop a safe, effective vaccine. This would be a disappointment, but even then, America could be well on its way to population-level immunity, perhaps reaching a Teflon critical mass by the fall of 2021. And the journey from now to then would probably not mean being cooped up indoors continuously for more than a year. "If we can't come out of our groundhog holes for more than 12 months," it's because the coronavirus is about as ferocious and noncompliant as it could possibly be, producing "some perfect storm of viral epidemic in which we can never relent," Noymer said.

Even in a vaccine-less world, reaching population-level immunity means that future outbreaks of COVID-19 should be far less damaging than the one the U.S. is currently confronting. The virus might, however, remain threatening and continue to circulate, infecting people like the cold or flu does. This wouldn't be ideal, but by then, life would be back to normal-though at the same time, completely changed.
*This story has been updated to clarify that it could be possible, under certain circumstances, for people who have already had the coronavirus to pass it on to others.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.

Joe Pinsker is a staff writer at The Atlantic, where he covers families and education.

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The Four Possible Timelines for Life Returning to Normal

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The coronavirus outbreak may last for a year or two, but some elements of pre-pandemic life will likely be won back in the meantime. Editor's Note: The Atlantic is making vital coverage of the coronavirus available to all readers. Find the collection here. Updated at 4:40 ET on March 30, 2020.

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Lecture on Where/How Pandemics Originate and Spread (thanks Justine!)

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Владимир Анненков

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Dr. Michael Greger on Pandemic Prevention | Infectious Diseases, Aids, Climate Change, Influenza

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NY Covid Hospital Doc Shares His (Comforting) Learnings

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13-minute Podcast -- Part I: Aerosols! Surfaces! Everything you need to know from one of the longest-published science magazines for lay people. Two questions (and answers) I appreciate, particularly as I try to navigate my way outside:
1. Can you catch it from someone who isn't in the same room as you? (One of my ongoing questions.) --> New vocab: fomites! (Pertinent for Amazon deliveries!)
2. People who feel fine now but will become ill 5-10 days from now are spreading the virus (the scenario with Rand Paul, who had no symptoms but tested positive, shutting down the Senate buildings).

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This is another in our series of coronavirus episodes of Scientific American 's Science Talk, posted on March 23, 2020. I'm Steve Mirsky.

In this two-part episode, our contributing editor W. Wayt Gibbs in Washington State-a state hit early and hard by COVID-19-reports on scientists' fast-evolving understanding of this new coronavirus and the probable trajectory of this pandemic.

Today, in part one, he focuses on why the new coronavirus is spreading so quickly and is so difficult to control.

Check back in tomorrow for part two, when Gibbs looks at computer models that are predicting how long we'll need to shut down large parts of society to prevent hospitals from being overwhelmed. He also looks at how emerging tests for immunity to the virus could pose thorny ethical issues in the months to come.

Wayt recorded this episode on March 22. The first voice you hear: Governor Jay Inslee of Washington.
JI: "It is not rhetorical or hyperbolic when I say that everyone needs to change their behavior, change the way that we live-temporarily-if we are going to prevent significant loss of life for the people we love in the state of Washington. And when I say everyone, I mean, frankly, everyone. Because we all are potential transmitters of this virus, and we all, to some varying degree, are potential victims of this virus."
WWG: That was Governor Jay Inslee, pleading with people in my state on March 20 to stay home and stay away from each other. All around the U.S.-and around the world-governors and mayors and prime ministers are urging, begging-in many places even ordering-their citizens to shelter in place.

But it's not easy to resist our hardwired desires to spend time with our friends, to visit our parents and grandparents, to go to work.

So here in Washington, like in lots of other places, compliance has been-kind of spotty. Traffic on some of the major highways here-a good proxy for human intermingling-is down only about 20 percent or so from normal.

But as scientists learn more about the SARS-CoV-2 virus and the COVID-19 pandemic, it's becoming apparent that we're facing a much more serious situation than most of us thought even a couple weeks ago.

Let me give you one example from here in Washington. On March 10, despite stern official warnings not to gather in groups, 56 people met for an event in Skagit County. All of them were apparently healthy at the time. But 10 days later, 43 of those 56 people have either been confirmed to have COVID-19 or are showing symptoms of the disease. Experts suspect that one or more people in the group was a so-called "supershedder," someone who has yet to show symptoms but is transmitting lots of infectious virus.

In this two-part episode, we'll look at several new research studies and new tests announced this week that may help answer four crucial questions.

Question 1: Can you catch this disease from someone who isn't in the same room as you?

Question 2: Can you catch it from somebody who isn't sick-and is there a way to test for that?

Question 3: What combination of shutdowns and closures will do the most to minimize the number of people who die from the pandemic? And how long will those tough restrictions need to continue?

And question 4: How will each of us know when we're immune and no longer need to worry about catching COVID-19 or giving it to someone else? And what will we do with that information once we have it?

Let's start with that first question: Do you have to come in contact with someone who has the virus-or with droplets they are spraying from a cough or a sneeze-to catch it?

Well, that's almost certainly the easiest way to get it. So keeping your distance from others greatly reduces your risk of infection.

But in a study out this week in the New England Journal of Medicine, researchers at a Montana biohazard lab run by the National Institutes of Health confirmed what many experts had feared: this coronavirus can also be infectious outside of a living body-in some cases for days.

The other night I watched the 2011 movie Contagion, which certainly has some eerie parallels to the present. There's a scene where Kate Winslet's character, a CDC disease investigator, explains why that kind of durability is so troubling in a virus.

[CLIP: Audio from Contagion]
KW: "So at this point I think we have to believe this is respiratory-maybe fomites, too." "What's that, fomites?" KW: "It refers to transmission from surfaces. The average person touches their face 2- or 3,000 times a day-three to five times every waking minute. In between, we're touching doorknobs, water fountains, elevator buttons and each other. Those things become fomites."
WWG: The NIH researchers tested whether the SARS-CoV-2 virus can spread via fomites-which, by the way, is how you actually pronounce it. They sprayed infectious droplets onto cardboard, stainless steel and plastic. Then they checked the spatter as time passed to see how quickly the viral particles dried out and fell apart.

On cardboard, it took a good four hours before the amount of live virus started to fall significantly, and the surface remained quite infectious eight hours later.

So when an Amazon box appeared on my front porch a couple days ago, I was glad to see that the delivery man was wearing gloves. But after I opened the box, I still went to the sink and washed my hands.

On stainless steel-think railings, shopping carts, gas pumps, jungle gyms-the coronavirus remained infectious for more than a day.

And on plastic-so, our pens, our credit cards, our keyboards and keypads-it stayed viable for two to three days.

Here in the Seattle area, store managers and bus operators have been wiping down surfaces more frequently and making disinfecting wipes available at the door for customers to use. We now know that should be standard practice everywhere.

Inside that box I received from Amazon was a set of white cotton gloves that I had ordered for me and my family to wear when we go out.

Tests have shown that a standard face mask really doesn't protect you from catching this virus because so much of the air you inhale leaks in around the edges rather than going through the filter. Wearing a mask is a nice courtesy, though, if you're going to be around others who may be vulnerable.

But a pulmonary surgeon advised me to wear cotton gloves, as they do at his hospital, because the natural fibers trap the virus and it dries out and becomes inactive. Also, I find that wearing gloves helps me remember to avoid touching my face.

So we can get infected from people we never even see-from the fomites they leave behind.

But now let's turn to that second question: Can you catch COVID-19 from someone who hasn't tested positive or even from someone who may feel perfectly healthy?

Studies seem to confirm that the answer is yes. In a paper that appeared on March 16 in the journal Science, an international group of researchers analyzed data on the outbreak in China in January. They concluded that only 14 percent of COVID-19 infections were documented, meaning that 86 percent-that's six out of seven cases-never showed up in the statistics as a confirmed case.

Here's what Jeffrey Shaman of Columbia University, one of the authors of that paper, said about that in a news briefing last week:
JS: "These undocumented infections were about half as infectious per person as a documented case who has more severe symptoms and may be shedding more. Because, however, there are many more of these undocumented cases, it's the undocumented infections that are driving the spread and growth of the outbreak."
Shaman says these undocumented cases are mostly quite mild.
JS: "And so most people may not recognize that they may think they have another cold, or they may not even really recognize that they're ill. If you were to project that number globally, given that we have 150,000 confirmed cases, it says that we're approaching close to a million infections globally. Generally, you're looking at about an order of magnitude more cases than have been confirmed."
WWG: Of course, every day the count of confirmed cases rises. But the idea is that if you take the count today and multiply by seven, that's a more realistic estimate of the number of infections to date.

So who is transmitting the virus? Obviously people who are very sick and have tested positive. Plus maybe seven times more people, many of them young, who have caught it but feel well enough that they wouldn't think to get tested or to self-quarantine.

And then there's a third group: the fast increasing numbers of people who are infected and who-five or 10 days from now-will fall ill and become a confirmed case but who feel perfectly fine at the moment.

In a preprint article published on March 18, researchers with the World Health Organization studied 94 COVID-19 patients in Guangzhou, China, to determine when they became infectious-and when they stopped shedding the virus. The scientists collected throat swabs from the patients as soon as they began showing symptoms and then tested them again every day for the following month.

They saw a lot of variation from patient to patient. But overall, the patients tended to become less infectious as their symptoms progressed. Through some calculations, the scientists concluded that these coronavirus patients shed the most virus, and were probably most infectious to others, up to two days before they started feeling ill. So these are people like Senator Rand Paul of Kentucky, who, we learned on March 22, has tested positive for COVID-19 even though he isn't yet feeling any symptoms.

These WHO researchers estimate that around half of the people who caught this virus in Guangzhou got it from someone who was still feeling healthy at the time. And other studies from China have documented cases where patients have fully recovered from COVID-19 but continued to test positive for the virus for more than a week after their symptoms disappeared.

This phenomenon of presymptomatic and postsymptomatic transmission really complicates efforts to contain this virus, in particular because it will be a long time before we have enough coronavirus tests to check people who aren't yet showing symptoms.

In a move to help ease shortages of coronavirus tests, the U.S. Food and Drug Administration last week gave emergency authorization to hospitals and labs to use a new automated test for COVID-19 that can detect infections in minutes rather than days. Cepheid, a biotech company in California, says it will start shipping the test kits this week.

The Cepheid test performs essentially the same real-time PCR process that existing tests do, just much faster, says Cepheid's chief medical officer David Persing:
DP: "So what we've developed is a reference-lab-quality test that can be run at the point of care in about 45 minutes or less. You take a sample, put it into this new cartridge that we've developed and, about 45 minutes later, you'll have the result. And that test can be run at the hospital as patients are being admitted. So the results are available much more quickly. And that means that those results will play into how those patients are managed: Who gets respiratory isolation. Who needs antibiotics? Who doesn't need antibiotics? Those kinds of decisions can be made in real time."
Persing says that while the test could be used for screening in the community-and may be sensitive enough to detect presymptomatic supershedders-initially it will be available only for hospitals to use on their patients and health care workers.
DP: "We think this will be a very important tool in being able to get rapid, actionable results to let patients know if they're carriers even if they're asymptomatic-to quarantine-and to know that they're being quarantined for a reason, not because they may have hay fever or some other cause. But really give them a reason for quarantine."
Faster, easier tests should help us get a better handle on the true extent of this pandemic. But these tests aren't perfect. A number of studies, including one done by scientists at Wuhan University in February, have found that these RT-PCR tests we're relying on today aren't sensitive enough to reliably catch the infection in its early stages. So a negative test result is no guarantee that you're not carrying the virus.

Nor does it tell you whether or not you are immune to the disease. But new tests for immunity are coming.

These characteristics of the new coronavirus-its ability to lie in wait on surfaces and to spread easily among people who feel fine or well enough-that is what make this virus so contagious and hard to stop, as Elizabeth Halloran of the Fred Hutchinson Cancer Research Center explained at a news briefing last week:
EH: "The basic reproductive number-that is, the average number of people that an average person infects at the beginning-is estimated to be about 2.5. And there are actually estimates that are higher. "That's before, of course, all this behavioral reduction and social distancing, which would reduce it. But it's going to be difficult, even if it does go down somewhat seasonally in the summer, to bring that down necessarily below one."
And until we can drag that reproductive number from 2.5 or so down to less than one, the pandemic will continue to accelerate.

In part two of this episode, we'll look at how computer models of the pandemic are predicting when we'll be able to emerge from our state of sequestration and start hanging out with each other again. Also in part 2, I'll update you on antibody tests for immunity to the virus that are now emerging from research labs. And we'll look at some tough ethical questions that society may confront as it uses this technology.

Until then, for Scientific American 's Science Talk, I'm Wayt Gibbs.

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COVID-19: How and Why the Virus Spreads Quickly

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Scientific American contributing editor W. Wayt Gibbs reports from the original U.S. epicenter of the coronavirus outbreak: Kirkland, Wash. In this installment of our ongoing series, he talks with researchers about the properties of the virus and why it spreads so quickly.

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From Amy Kemner (MA, Epidemiology). [Lisa's notes]

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From Amy Kemner (MA, Epidemiology). [Lisa's notes]

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Part II: 16-minute podcast. Computer models that show how long shutdowns must be to avoid hospital overload. Pertinent modeling numbers from Imperial College London's forecast mechanism:

R = Reproduction Number (# of infections resulting from one case) --> now estimated 2-3 ppl on average, ranges from no infections to "super-spreaders" *Note: reducing # of ppl any single person contacts reduced R in pandemic
Serial Interval  = average time of infection before someone passes to someone else (4 days for current pandemic). Many cases passing from asymptomatic people.

Uncontrolled/unmitigated pandemic conditions: estimated infection of 80% of population, with  pandemic petering out by September. Following China's 3-month lockdown, will test re-introduction, but *within a few weeks of lifting restrictions, without widespread/herd immunity (exposure or vaccine, which is 18 months out), epidemic will re-seed and grow again.
Developing a serologic test will enable us to determine who has developed antibodies.

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SM: This is part two of this episode in our series of coronavirus editions of Scientific American 's Science Talk, posted on March 24, 2020. I'm Steve Mirsky.

In part one of this episode, which we posted yesterday, contributing editor W. Wayt Gibbs reported on research showing that it's likely that most people are catching COVID-19 from others who feel fine or think their mild symptoms are due to allergies or a cold. And you can probably also pick up the infection from virus deposited many hours earlier on inanimate objects like a gas pump or a credit card or a pen.

Now, in part two, Gibbs talks with computational epidemiologist Lauren Ancel Meyers of the University of Texas about how scientists are building highly detailed computer models of the pandemic to predict when we'll be able to ease up on social distancing. He also updates us on tests for immunity to the virus that are now coming out of research labs. Society, he warns, could face some tough ethical questions if we start treating people who are immune differently from those who are not.

Wayt recorded this episode on March 23.

WWG: I posed four crucial questions about the coronavirus pandemic in part one of this episode. Let's pick up now where we left off, with question three:

What combination of shutdowns, closures and quarantines will most effectively reduce the death toll from COVID-19?

And what does the end game look like for this pandemic? When can we responsibly start reopening our office buildings, schools, restaurants, theaters and stadiums?

There are no certain answers to these questions yet. But we aren't completely in the dark.

For decades, scientists have studied how infectious epidemics spread and eventually end. They've built and tested mathematical models and software that can replicate that behavior in a computer.

Of course, no model can capture the full complexity of the real world. And there is quite a bit about COVID-19 that we still don't know. So the predictions these models make will never be 100 percent accurate.

That said, when a wide range of models all start to point in the same direction-as, to take a different example, global warming models now do-then we need to pay attention.

Last week, a large team of epidemiologists at the [MRC] Center for Global Infectious Disease Analysis at Imperial College London released a report with predictions from one of the most sophisticated models of this kind. They took software they had already developed and validated for pandemic influenza and then adapted it to make forecasts of the COVID-19 pandemic for Great Britain and the United States. The results in that report make for pretty sobering reading.

I'll talk about those in a minute.

But first it's important to understand a few key numbers that these models use to predict how the disease will spread. Numbers like how many others get infected by each COVID-19 case on average-that's called the reproduction number, R. Another is the average number of days between someone catching the virus and passing it on to someone else-that's called the serial interval. Hospitalization and mortality rates for each age group are also important. I spoke with a computational epidemiologist who has been working to improve estimates of these numbers so that model predictions can be more accurate.
LAM: "My name is Lauren Ancel Meyers. I'm a professor at the University of Texas at Austin. And I am a pandemic modeler. My background is in mathematical modeling of infectious disease dynamics. "Estimates for the basic reproduction number have ranged a little bit, but many have been in the range of two to three, meaning that the average infected person early in an uncontrolled epidemic is infecting maybe two to three other people, and that's an average. "The variation in the number of secondary cases can be quite wide. You can have some individuals who don't spread disease to anyone-or maybe to just one other person-and then other individuals who are super spreaders, people who are spreading to an unusually high number of other people. "If you think about the reproduction number, there are really two parts to it. There is how intrinsically contagious you are. Is it a disease that leads to coughing, sneezing-causes you to be ill in a way that spreads virus? And then the other part of it is how many people you actually come in contact with. "And you can reduce the reproduction number by changing either one of those. And what social distancing interventions do is they're reducing the opportunities for transmission. They're reducing the contacts that take place between infected and susceptible people."
WWG: In a paper published on March 19 in the journal Emerging Infectious Diseases, Meyers and her colleagues in Texas, France and China used case histories of more than 400 COVID-19 patients to determine how quickly the virus hopped from one person to the next.
LAM: "So that's called the serial interval. We estimated that the average length of the serial interval was around four days. So that's pretty fast. And moreover, we found that over 10 percent of those-the secondary case actually reported feeling symptoms before the primary case, meaning that the infector, the primary case, probably was contagious and spread disease before they even knew they were sick, before they started feeling ill."
WWG: The model Neil Ferguson and his team at Imperial College developed actually used a slower serial interval of six and a half days, and it explored the effects of reproductive numbers ranging between 2 and 2.6.

The program essentially creates a virtual country in a computer, complete with virtual cities, schools, workplaces and hospitals, all based on official statistics for Great Britain. As it runs, it simulates all the interactions that govern how an infectious disease spreads over months and years.

To estimate how effective social distancing and other control measure will likely be, they first simulated an imaginary, worst-case scenario in which we did none of those things and simply let COVID-19 rampage through the U.S. unchecked. The results from that simulation show why no country should contemplate taking a hands-off approach to this pandemic.

The model predicts that without quarantines or social distancing, mortality from the pandemic would skyrocket for the new few months, peak in June or July, and then decline through September, in a steep bell curve. If we took no measures to flatten that bell curve, the model predicts that over 80 percent of the U.S. population would be infected, and fatalities would number in the millions.

And that is why the U.S. and governments around the world have already taken big steps to flatten the curve, and the model predicts that they can be very effective. In fact, the main point of this study was not to scare people but to try to understand which combinations of control measures are likely to be most effective.

The epidemiologists looked at various options combining five different control measures, including restrictions many of us are now living with: school and university closures, voluntary quarantines of the sick and their contacts for two weeks, and prohibition of social gatherings that are restrictive enough to reduce contacts among individuals by 75 percent outside of work and the home.

There's some good news in these simulation results. It looks like closing schools, isolating confirmed cases and getting everyone to practice social distancing should drive the number of critical COVID-19 cases down to a level our health care systems can handle. The authors write that because it remains to be seen how people will respond to these controls, "it is difficult to be definitive about the likely initial duration of measures that will be required, except that it will be several months."

But there's also some bad news. In these simulations, infections start to shoot up quickly as soon as we let people congregate once again. The model predicts that within a few weeks of lifting the restrictions, we're pretty much back where we started.

So until immunity to the disease becomes common, flattening the curve is like stepping on a balloon. You can change the shape of it by a lot, but the volume-the total number of people who will ultimately catch this virus-that is likely to remain about the same. And that's because the epidemic can be reseeded and grow again by anyone who still has it, anywhere in the world-unless you can chase down every infected person and isolate them before they infect someone else.

The researchers write: "To avoid a rebound in transmission, these policies will need to be maintained until large stocks of vaccine are available to immunise the population-which could be 18 months or more."

Other pandemic experts have come to similar conclusions. Here's Ira Longini of the University of Florida:
IL: "It's probably only a vaccine that can really control the epidemic to a large extent by reducing the susceptibility of vaccinated people and also, if they do get infected, reducing the transmissibility to others."
WWG: After reading the report from Imperial College, Lauren Meyers had this to say:
LAM: "I think that their study is very plausible. I think there's a lot of uncertainty about when and how we will be able to relax some of these measures and yet keep this threat contained. "I think that as the modeling community and public health community coalesce around this understanding that this is going to be a very challenging virus to control going forward, I think we are turning our attention to really thinking in a quantitative way and an innovative way about how we can, in the long run, continue to contain the virus while not having such a devastating social and economic cost on our societies. "And I don't think we have the answers yet, but part of the answer will probably be maybe slowly relaxing social distancing measures, allowing us to get back to life as normal slowly, being very vigilant about testing in isolation and quarantine of cases and their contacts if, and when, disease is reintroduced into a community that has succeeded in controlling it."
WWG: China is now testing that approach by gradually loosening the intense lockdown it has imposed since January on much of its population. Let's hope that what happens next in China proves that the modelers missed something important and that it is actually possible to end the epidemic in a large country even though the vast majority of the population still lacks immunity to the disease.

It's frustrating that no one can predict when a vaccine will be available. Numerous labs around the world are working at a breakneck pace to create and test vaccine. But no one has succeeded yet in making vaccines against the two other deadly coronaviruses that cause SARS and MERS.

Meyers says that, as we wait for a vaccine, a kind of herd immunity may well build naturally in the population, as more and more people become infected and then recover.
LAM: "As immunity builds up in a population, the reproduction number starts to decline. There are just not as many options for transmission. And when the reproduction number gets to a point that is below one, that means that every infected case is expected to infect fewer than one other person. And because of that, the epidemic will start to peter out and eventually disappear."
WWG: But how will we know how much herd immunity has built up? A serologic test-one that looks for antibodies for the disease inside the blood-might help with that. Here's Longini again:
IL: "We need a serologic test that's specific to this virus-and we don't have one right now-so we could find out what proportion of the population was infected and how much herd immunity there may be out there, keeping in mind the caveat that immunity may not be durable."
WWG: So now we've arrived to the last of those crucial questions I posed at the beginning-how each of us will know when we have immunity and no longer need to worry about catching COVID-19 or giving it to someone else-and also the question of what we will do with that information once we have it.

Researchers have already shown that people who are infected with this coronavirus do develop antibodies to it. BioMedomics, a company in North Carolina, has even developed a fast test for those antibodies. It works much like a pee-on-a-stick pregnancy test, except the technician places a small drop of blood, along with a few drops of buffer solution, onto the paper strip. Fifteen minutes later, lines appear that tell you whether you have the IgG antibodies that reveal you were exposed to a coronavirus at some point in the past.

The current version of this test will read positive even if you've been exposed to any coronavirus, including the four mostly harmless human coronaviruses that cause the common cold. But in the near future, it's likely that rapid diagnostics like this will be able to prove that someone has some immunity to COVID-19.

But we don't know yet whether people who have antibodies against SARS-CoV-2 could still get reinfected by the virus and possibly give it to others for a day or two before their immune system wipes it out.

Researchers in China reported this week some encouraging results from a study on rhesus monkeys. Two weeks after the monkeys were infected with COVID-19, became sick and recovered, the scientists tried to reinfect the animals with the virus. The infection didn't take.

That was a small and short study, but it gives some reason to hope that the same will be true for people as well. We'll know it isn't if people who have recovered from COVID-19 start coming down with the disease a second time.

But if immunity to COVID-19 is long-lasting and does prevent people who have antibodies to the virus from infecting others, then we should think very carefully about how we use these antibody tests.

A paper in the Journal of Medical Virology last month, written by doctors in China affiliated with BioMedomics, suggested that the 15-minute, paper-strip tests could be administered at train stations and airports to screen passengers.

But consider the ripple effects of policies that allow only those who can demonstrate immunity to COVID-19 to resume travel, to go to theaters and restaurants, to work closely with others-while those who have yet to catch the virus cannot do any of those things.

Will some nations effectively set up two-tiered societies, creating powerful incentives for some people-young people in particular-to infect themselves in order to develop immunity and escape the economic and psychological burdens of social distancing?

Throughout the history of public health, there's been a tension between the inequity of individual quarantines and the protection of society at large from greater harm. Now many states have taken the hard and unprecedented decision to effectively put everyone under quarantine. But if these restrictions stretch on for month after month after month-as the models suggest they might need to-governments will also face hard decisions about how to lift those quarantines-selectively or universally, temporarily or permanently. Now is the time to start plotting a smart-and equitable-end-game strategy for this pandemic.

For Scientific American 's Science Talk, I'm Wayt Gibbs.

SM: And I'm Steve Mirsky. Just wanted to remind you that all of our coronavirus coverage is available for free on our Web site: www.ScientificAmerican.com.

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COVID-19: Predicting the Path and Analyzing Immunity

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Scientific American contributing editor W. Wayt Gibbs continues to report on the coronavirus outbreak from his home in Kirkland, Wash., site of the first U.S. cases. In this installment, he talks with researchers about what their models show for the future of the pandemic and on research to create tests to see who has developed immunity.

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From Mairi Luce: World Stats Compiled (3/24, stats updated in real time)

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From Mairi Luce: World Stats Compiled (3/24, stats updated in real time)

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I actually found the "recovered" field to be useful/comforting to add perspective.

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COVID - Coronavirus Statistics - Worldometer

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Daily and weekly updated statistics tracking the number of COVID-19 cases, recovered, and deaths. Historical data with cumulative charts, graphs, and updates.

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National Institute for Health study re: C-19 viability on surfaces (3/17)

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National Institute for Health study re: C-19 viability on surfaces (3/17)

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"Detectable in aerosols for up to three hours, up to four hours on copper, up to 24 hours on cardboard and up to two to three days on plastic and stainless steel. The results provide key information about the stability of SARS-CoV-2, which causes COVID-19 disease, and suggests that people may acquire the virus through the air and after touching contaminated objects."

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SARS-CoV-2 stability similar to original SARS virus.

What

The virus that causes coronavirus disease 2019 (COVID-19) is stable for several hours to days in aerosols and on surfaces, according to a new study from National Institutes of Health, CDC, UCLA and Princeton University scientists in The New England Journal of Medicine. The scientists found that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was detectable in aerosols for up to three hours, up to four hours on copper, up to 24 hours on cardboard and up to two to three days on plastic and stainless steel. The results provide key information about the stability of SARS-CoV-2, which causes COVID-19 disease, and suggests that people may acquire the virus through the air and after touching contaminated objects. The study information was widely shared during the past two weeks after the researchers placed the contents on a preprint server to quickly share their data with colleagues.

The NIH scientists, from the National Institute of Allergy and Infectious Diseases' Montana facility at Rocky Mountain Laboratories, compared how the environment affects SARS-CoV-2 and SARS-CoV-1, which causes SARS. SARS-CoV-1, like its successor now circulating across the globe, emerged from China and infected more than 8,000 people in 2002 and 2003. SARS-CoV-1 was eradicated by intensive contact tracing and case isolation measures and no cases have been detected since 2004. SARS-CoV-1 is the human coronavirus most closely related to SARS-CoV-2. In the stability study the two viruses behaved similarly, which unfortunately fails to explain why COVID-19 has become a much larger outbreak.

The NIH study attempted to mimic virus being deposited from an infected person onto everyday surfaces in a household or hospital setting, such as through coughing or touching objects. The scientists then investigated how long the virus remained infectious on these surfaces.

The scientists highlighted additional observations from their study:

If the viability of the two coronaviruses is similar, why is SARS-CoV-2 resulting in more cases? Emerging evidence suggests that people infected with SARS-CoV-2 might be spreading virus without recognizing, or prior to recognizing, symptoms. This would make disease control measures that were effective against SARS-CoV-1 less effective against its successor.

In contrast to SARS-CoV-1, most secondary cases of virus transmission of SARS-CoV-2 appear to be occurring in community settings rather than healthcare settings. However, healthcare settings are also vulnerable to the introduction and spread of SARS-CoV-2, and the stability of SARS-CoV-2 in aerosols and on surfaces likely contributes to transmission of the virus in healthcare settings.

The findings affirm the guidance from public health professionals to use precautions similar to those for influenza and other respiratory viruses to prevent the spread of SARS-CoV-2:

Avoid close contact with people who are sick.

Avoid touching your eyes, nose, and mouth.

Stay home when you are sick.

Cover your cough or sneeze with a tissue, then throw the tissue in the trash.

Clean and disinfect frequently touched objects and surfaces using a regular household cleaning spray or wipe.

Article

N van Doremalen, et al. Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. The New England Journal of Medicine. DOI: 10.1056/NEJMc2004973 (2020).

Who

NIAID Director Anthony S. Fauci, M.D., and Vincent Munster, Ph.D., a principal investigator in NIAID's Laboratory of Virology, are available to comment on this study.

This media availability describes a basic research finding. Basic research increases our understanding of human behavior and biology, which is foundational to advancing new and better ways to prevent, diagnose, and treat disease. Science is an unpredictable and incremental process- each research advance builds on past discoveries, often in unexpected ways. Most clinical advances would not be possible without the knowledge of fundamental basic research.

NIAID conducts and supports research - at NIH, throughout the United States, and worldwide - to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on the NIAID website.

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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New coronavirus stable for hours on surfaces

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SARS-CoV-2 stability similar to original SARS virus. The virus that causes coronavirus disease 2019 (COVID-19) is stable for several hours to days in aerosols and on surfaces, according to a new study from National Institutes of Health, CDC, UCLA and Princeton University scientists in The New England Journal of Medicine.

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Interview with  Prof Deenan Pillay (3/24 -- The Guardian)

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Interview with  Prof Deenan Pillay (3/24 -- The Guardian)

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This is super useful to understand both the chemistry of viral transmission and the differences between research outcomes, media headlines, etc. This one adds "lipid envelope" to my understanding (breaking it is why handwashing is effective in de-activating the virus).

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Covid-19: how long can it survive outside the body?

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Sarah Boseley speaks to Prof Deenan Pillay about how the virus contaminates surfaces outside the human body