This doctor on YouTube claims that the SARS-CoV-2 virus can float in the air for up to 3 hours.

If it lands in the air, the virus can land on a particle and stay floating there for up to 3 hours.

Is that true?


Author's note, 11 July 2020:

This answer was originally written in late March of 2020, at which point the coronavirus pandemic was, in many countries, far from its peak. In the intervening time, there have been various studies continuing to investigate the possible spread of coronavirus via aerosols and respiratory droplets. I haven't taken a detailed look at recent studies, so I'm not ready to update this, but the takeaway is that our understanding of the virus has gotten better, and it's possible that the study discussed below can now be corroborated or refuted. The underlying point - that the video is based on one set of data points which arguably don't mimic real-world conditions well - is of course still valid.

It's possible, but more research is needed.

Tl;DR: The claim in the video appears to be based on a single recent study of the median half-life of SARS-CoV-2 (more on that below). That study was based on the measurements of virus concentrations over only a short period of time and under conditions unlikely to be found in the real world. While the study's results indicate the virus can stay around for hours in the air, that doesn't necessarily jibe with what we've been seeing around the world.

A later, abbreviated version of the preprint Laurel mentions, published in the New England Journal of Medicine as Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1, measured the half-lives of SARS-CoV-1 and SARS-CoV-2 in a variety of environments, including aerosols, cardboard, and plastic. This version lists the median viable half-lives of SARS-CoV-2 and SARS-CoV-1 as 1.09 hours and 1.39 hours, respectively, with 97.5% upper confidence limits of 2.64 hours and 2.43 hours. I'm not sure how to account for the discrepancy between the two versions of the paper.

(Note that this is a half-life, so even if we take those median half-lives as the actual half-lives of the viruses, some samples stayed in the air for much longer than that - the half-life is not an upper limit. The paper does not provide an upper limit; the virus was only studied for 3 hours.)

Now, the aerosol measurements were conducted at 65% relative humidity and 21-23°C. This is important to note, because previous research on SARS-CoV-1 indicates that higher humidity and higher temperature can severely decrease the virus half-life (and vice versa for lower humidity and lower temperatures).

Another thing to bear in mind is that coronaviruses are not expected to spread primarily through aerosols, but rather in droplet form. To quote a microbiologist not associated with the study:

The NIAID study "is measuring virus under ideal conditions and with a lot of virus," said microbiologist Benjamin tenOever of the Icahn School of Medicine at Mount Sinai. "So their results are all likely to be overestimates. That said, I think those values should at least be used to let people know that things like subway poles can harbor virus for more time than I would have considered possible," because an aerosol that encounters a solid object can stick to it. "Washing hands is more important than ever."

And, as noted earlier in that article:

"If it could easily exist as an aerosol, we would be seeing much greater levels of transmission," said epidemiologist Michael LeVasseur of Drexel University. "And we would be seeing a different pattern in who’s getting infected. With droplet spread, it’s mostly to close contacts. But if a virus easily exists as an aerosol, you could get it from people you share an elevator with."

According to the Centers for Disease Control and Prevention, that is not happening.

In other words, let's take the study's half-life results - regardless of the version of the paper - with a grain of salt. They were derived under artificial conditions, not real-world environments, and it's not clear that aerosol transmission is significant at all, given actual data. More study is definitely needed.

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    @DanielRHicks That's not what doctors and epidemiologists are saying, as I've noted in this answer. I'm curious as to why you disagree. – HDE 226868 Mar 26 at 22:24
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    @DanielRHicks I would recommend doing some reading; current information suggests that respiratory droplets and contact with surfaces. If you touch a surface with the virus and then touch your face, eyes, mouth, etc., it's quite easy for it to enter your respiratory system - hence why washing hands is exceedingly important. – HDE 226868 Mar 26 at 22:29
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    @DanielRHicks - You appear to be conflating aerosol transmission and droplet transmission. They are different things. – David Hammen Mar 27 at 10:18
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    @user2705196 Respiratory droplets and aerosols are two completely different things - see one of the papers I linked to that makes the distinction. The two terms are not the same, and the CDC does not mention aerosols. – HDE 226868 Mar 27 at 21:46
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This is probably referencing Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. (Note that CoV-1 is the 2003 Coronavirus.) They used a “Collison nebulizer” to get the virus into the air and took samples periodically, with the last one being 3 hours later.

According to the study:

We found that viable virus could be detected in aerosols up to 3 hours post aerosolization [...] HCoV-19 and SARS-CoV-1 exhibited similar half-lives in aerosols, with median estimates around 2.7 hours.

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    I find the quote quite hard to understand. Could you summarise, and provide a more succinct answer to the OP's question, so that perhaps other readers like myself can learn more from this answer? – theonlygusti Mar 26 at 15:07
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    @theonlygusti - I read the quote as saying that if there's absolutely no airflow and you wait for 3 hours, there will be 6 times less SARS-CoV-2 in the air than when you started. The study simply didn't run for longer than 3 hours, but they tried it thrice. In real life conditions, the aerosol will probably be gone faster. Where to? I don't want to know. – Jirka Hanika Mar 26 at 15:29
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    @theonlygusti: there was a recent Epidemics podcast that covered the topic a week ago in human intelligible terms. – Denis de Bernardy Mar 26 at 15:47
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    Note that if the half-life is 2.7 hours, then the virus will still be present for much longer at decreasing concentration. – chrylis -cautiouslyoptimistic- Mar 26 at 21:27
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    @HDE226868 - Lack of data. Without much more comprehensive measurements involving different concentrations and longer test durations, as well as assumptions regarding which specific concentrations are infectious to humans, you shouldn't even assume that "half-life" (i.e. exponential decrease) is the right model to use, and that any non-zero concentration is sufficient for infectivity. – Jirka Hanika Mar 27 at 6:34

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