Gates Package — page 980

The good news is that COVID's airborne proclivities could be a lot worse. It appears that the virus is able to stay in the air for several seconds, and perhaps up to a minute. The virus that causes measles, on the other hand, can stay in the air for hours. To understand why viruses get transmitted through the air, we need to talk about your breath. Whenever you talk, laugh, cough, sing, or simply breathe out, you exhale. We tend to think of the stuff we're exhaling as air, but it contains a lot more than air. Your breath is filled with tiny globs of liquid, a mix of mucus, saliva, and other secretions from your respiratory tract. These globs are grouped into two categories by size: The larger ones are known as droplets, and the smaller ones are called aerosols. The dividing line between them is typically 5 micrometers, which is roughly the size of the average bacterium. Anything bigger than that is a droplet, and anything smaller is an aerosol. Droplets, being on the larger side, typically contain more virus than an aerosol, which makes them a better mechanism for transmission. On the other hand, because they're relatively heavy, they don't make it more than a few feet from your mouth or nose before falling to the ground. The surface that a droplet lands on becomes what's called a fomite, and how long the fomite is able to transmit the virus depends on several factors, including the type of pathogen and whether you sneezed or coughed it out (in which case it's more protected because it's covered in your mucus). Studies of COVID's ability to survive on fomites show a wide range of results, from an hour or two to a few days. There are undoubtedly some instances in which people picked up the virus by touching an infected surface, but they are certainly a small fraction of all cases.