Van Kerkhove was making a useful point about the term “asymptomatic” being applied too broadly; in the midst of a pandemic, though, it needed to be better expressed. The larger damage was done when she combined that observation about terminology with what came across as a general statement about who is contagious. In doing so, she undermined the message that, for example, people should wear masks in public even if they don’t think they are ill. (After all, as she herself acknowledged, they are the people who define themselves as asymptomatic.) This was especially harmful because, as both she and Ryan noted in the Facebook event, studies have shown that an infected person’s “viral load”—the amount of SARS-CoV-2 in their body—seems to be highest around the time that symptoms first appear. This raises the possibility that people who appear to be asymptomatic but are, in fact, presymptomatic may be particularly contagious.

Also, the virus is present in the upper respiratory tract, so it appears that it can spread simply through, as Ryan put it during the event, “singing, speaking loudly, exertion, maybe in a gym . . . shouting in a night club because you can’t hear your friend.” (Coughing and sneezing, of course, are likely to spread virus-bearing droplets farther through the air, which is a reason that symptomatic patients could infect more people; an unanswered question is how much each group drives the pandemic.) Someone might go to a restaurant “feeling O.K.,” but their “viral load could be actually quite high.” (In a key epidemiological study showing how the virus spread from table to table in a restaurant in China, the initial patient didn’t report symptoms until hours after having eaten there.) Ryan emphasized that this was a reason for wearing masks. “There is this period of time when, you know, even a professor of infectious diseases themselves wouldn’t know that I’m getting COVID,” Ryan said. “There is that hours or days in which you’re not that unwell, or you could be becoming unwell, you’re not aware of your status, and it’s because the disease can spread at that moment that the disease is so contagious. That’s why it’s spread around the world in such an uncontained way. It’s because it’s hard to stop this virus.”