Ok, apparently this is the hill I'm going to die on.

Up through roughly April-May 2020, many, if not most, epidemiologists and virologists believed that masks would not help the situation: they thought respiratory viruses were spread through large droplets produced by symptomatic individuals and that physical separation, sanitation, and behavior would work as well as trying to convince people to were useful masks consistently and correctly. (Earlier today, I walked past a woman wearing a bandana tied around her head. Below her nose. Why!?)

After that time, reports began to appear showing coronavirus could be spread asymptomatically, by normal breathing and speech, in an aerosol form that could stay airborne for long times. Under those situations, masks are the only solution.

The "ensure that enough protective equipment was available for frontline health workers" thing was mostly a response to "but it couldn't hurt" thinking.

"Then there is the infamous mask issue. Epidemiologists have taken a lot of heat on this question in particular. Until well into March 2020, I was skeptical about the benefit of everyone wearing face masks. That skepticism was based on previous scientific research as well as hypotheses about how covid was transmitted that turned out to be wrong. Mask-wearing has been a common practice in Asia for decades, to protect against air pollution and to prevent transmitting infection to others when sick. Mask-wearing for protection against catching an infection became widespread in Asia following the 2003 SARS outbreak, but scientific evidence on the effectiveness of this strategy was limited.

"Before the coronavirus pandemic, most research on face masks for respiratory diseases came from two types of studies: clinical settings with very sick patients, and community settings during normal flu seasons. In clinical settings, it was clear that well-fitting, high-quality face masks, such as the N95 variety, were important protective equipment for doctors and nurses against viruses that can be transmitted via droplets or smaller aerosol particles. But these studies also suggested careful training was required to ensure that masks didn’t get contaminated when surface transmission was possible, as is the case with SARS. Community-level evidence about mask-wearing was much less compelling. Most studies showed little to no benefit to mask-wearing in the case of the flu, for instance. Studies that have suggested a benefit of mask-wearing were generally those in which people with symptoms wore masks — so that was the advice I embraced for the coronavirus, too.

"I also, like many other epidemiologists, overestimated how readily the novel coronavirus would spread on surfaces — and this affected our view of masks. Early data showed that, like SARS, the coronavirus could persist on surfaces for hours to days, and so I was initially concerned that face masks, especially ill-fitting, homemade or carelessly worn coverings could become contaminated with transmissible virus. In fact, I worried that this might mean wearing face masks could be worse than not wearing them. This was wrong. Surface transmission, it emerged, is not that big a problem for covid, but transmission through air via aerosols is a big source of transmission. And so it turns out that face masks do work in this case.

"I changed my mind on masks in March 2020, as testing capacity increased and it became clear how common asymptomatic and pre-symptomatic infection were (since aerosols were the likely vector). I wish that I and others had caught on sooner — and better testing early on might have caused an earlier revision of views — but there was no bad faith involved."

"I’m an epidemiologist. Here’s what I got wrong about covid."(https://www.washingtonpost.com/outlook/2021/04/20/epidemiolo...)