It’s summer. It’s hot. And COVID-19 is rampaging across the nation at rates higher than ever before. There was never really any reason to believe that SARS-CoV-2 would fold up its tent and go home for the summer. It’s not a flu virus, and early evidence showed that COVID-19 seems to spread at least as well in warm, humid conditions as does in cold and dry conditions. Donald Trump’s repeated assertions that the virus would go away, either “by magic” or otherwise, have been proven false. So much for the instinct versus science debate … not that it ever was a debate.
But there is a matter of genuine dispute over COVID-19, and that has to do with the manner of transmission. For some weeks, there have been a series of articles and letters being batted back and forth over the extent to which COVID-19 is an airborne disease, with the latest letter backed by 240 scientists who want the World Health Organization (WHO) and other authorities to revise their recommendations to “recognize the potential for airborne spread of COVID-19.” However, the way this letter is being reported can be misleading—and this time, the scary music being applied to this dispute is not really deserved.
No one is disputing the assertion that COVID-19 is a respiratory illness, or that the primary means of transmission of the disease is by droplets spread when people cough, talk, sing, or go on an extended tirade about why wearing a mask violates their constitutional rights (even if they don’t have a clue what’s in the Constitution). In fact, one of the few good news items of the last few months is the realization that the odds of catching COVID-19 from surfaces appears to be considerably lower than originally expected. Don’t stop washing your hands. But if you have not yet created a simulated airlock in which your groceries are de-bagged, scrubbed, and left to air in an isolated “warm zone” before being allowed into the house proper (the way that, ahem, someone might have done) … you can probably skip that. Likewise, bringing in the mail and opening that latest box from some online source are also relatively safe activities.
The question over airborne transmission isn’t whether or not COVID-19 can be spread person to person through the air, but just how easily that occurs. And what that comes down to is a matter of how many virus particles someone needs to breathe in to have a reasonable chance of catching the disease. That, in turn, involves droplets. Droplets large, and droplets small.
When someone breathes, coughs, sings, laughs, or sneezes, they produce droplets in a wide range of sizes. The largest droplets are the most dangerous simply because they contain more copies of the virus—easily millions in a single drop—and because the moisture in these drops helps protect the virus against the damage that can occur when the droplet dries. However, these large droplets do what large droplets do: they fall. So unless someone is belting out a rock ballad, or bellowing over nasty leakers in his Cabinet, these droplets tend to fall within a foot or two of the source. Social distancing is the best protection against these larger droplets, and masks do a good job of protecting against them when they do make an impact.
At the far end of the scale are the kind of droplets that we exhale on every breath—droplets so small as to be invisible, each one of which may carry a viral load that is more like dozens than millions. These droplets are so small that they respond more to air currents than gravity. However, they also have such a high surface area to volume ratio that they essentially dry up almost instantly, particularly in low-humidity indoor air. For want of a better term, these droplets become “dust” drifting around the room.
There are diseases where even the tiny viral load obtained by breathing in a little of this viral dust is enough to spark infection. Measles is one of those. If someone with measles simply walks through a room where a dozen people who are not immune to measles are standing, odds are good that every single person who remains in that room for any length of time will come down with measles. The godawful smallpox has a similar ease of transmission. But no one is arguing this is true of COVID-19.
Where the argument falls on COVID-19 is in the middle ground. Specifically, the concern is over aerosols—droplets that may travel an extended distance and linger in the air considerably longer than the larger droplets recognized as spreading COVID-19. Rather than dropping off a foot or two from the source, these droplets may travel six feet or more. In fact, they may even make a few circuits of a room before either hitting the ground or drying.
So, are there micro-droplets containing SARS-CoV-2 that are released by normal breathing, talking, and coughing that are 1) small enough to remain airborne at distances considerably larger then six feet and 2) pose an infection risk to others? As the letter posted by the concerned scientists puts it, this is "beyond all reasonable doubt."
That certainly sounds bad. It is bad. However, it’s not the note of pure doom it may seem to be.
Much of the argument is really about some details of how the WHO classifies diseases, including not just COVID-19, but the flu, which have to do with recommended procedures and may affect things like where medical supplies get distributed. It’s important, but it’s not the No. 1 concern of most people at the moment.
The impact on how we deal with COVID-19 appears to be this: social distancing, hand-washing, and wearing a cloth mask most of the time is important in reducing the spread of COVID-19. However, even all of the above is not an absolute guarantee of protection. That’s particularly true in situations where people are staying for extended periods in poorly ventilated places. The researchers cited an instance of a spreading event that took place at a restaurant in China where diners were kept well spaced apart, the wait staff was carefully monitored, and the restaurant still became an apparent spreading center. The same thing applies with churches and other types of prolonged meetings. Even when people were kept at a distance, new incidents of COVID-19 popped up.
The most obvious take-away from this is to stay away from that kind of situation. COVID-19 isn’t measles. It does not linger in the air for hours after an infected person has passed through a room. It may not even linger for minutes. But if you’re sharing a room with multiple infected people, odds are you are going to begin respirating infected aerosol particles. Do that long enough, and you can pick up enough of a viral load to trigger an infection.
The other big takeaway comes down to masks. Cloth masks and disposable surgical masks have proven to be highly effective in reducing the spread of COVID-19. That remains true. However, for essential workers who have to work in an indoor environment—especially those like hospital staff working in an area where they know infected patients are present—the use of N95 masks that can block these smaller aerosols is essential. And, with another looming shortage of personal protective equipment, that’s a very good reason why most people should leave the N95 masks to those in situations where they really need them.