Topic: If the coronavirus is really airborne, we might be fighting it the wrong way
This was the week airborne transmission became a big deal in the public discussion about covid-19. Over 200 scientists from around the world cosigned a letter to the World Health Organization urging it to take seriously the growing evidence that the coronavirus can be transmitted through the air. WHO stopped short of redefining SARS-CoV-2 (the virus that causes covid-19) as airborne but did acknowledge that more research is “urgently needed to investigate such instances and assess their significance for transmission of COVID-19.”
“I honestly don’t know what people are waiting for,” says microbiologist Chad Roy of Tulane University in the US. “It doesn’t take WHO coming out to make a proclamation that it’s airborne for us to appreciate this is an airborne disease. I don’t know how much clearer it needs to be in terms of scientific evidence.”
So what does “airborne” really mean in this context? It’s basically an issue of size. We’re pretty sure that SARS-CoV-2 is spread through tiny droplets that contain viral particles capable of leading to an infection. For a virus to be airborne, however, means a few different things, depending on the expert you’re talking to. Typically it means it can spread via inhalation over long distances, perhaps even through different rooms, of small particles known as aerosols.
“That’s why when you ask some of the professionals if the virus is airborne, they’ll say it’s not, because we’re not seeing transmission over those sorts of distances,” says Lisa Brosseau, a retired professor of public health who still consults for businesses and organizations.
There is also some debate on what we mean by “aerosol.” The droplets that carry viral particles through the air can come in all sorts of sizes, but while the larger ones will drop quickly to the ground or other surfaces, the smaller ones (just a few microns across) can linger in the air for a while, giving them a chance to be inhaled. The word is mostly used to describe these smaller particles, although Brosseau would prefer the term “aerosol transmission” to cover the entire gamut of inhalable viral particles being expelled into the air—large and small alike.
If SARS-CoV-2 is airborne, it’s far from the only disease. Measles is notorious for being able to last in the air for up to two hours. Tuberculosis, though a bacterium, can be airborne for six hours, and Brosseau suggests that coronavirus superspreaders (people who seem to eject a larger amount of the virus than others) disseminate the virus in patterns that recall the infectiousness of tuberculosis.