The Case Against Cloth Masks

I have been a substantial advocate for mask-wearing in public places, even unto wearing cloth masks as a substitute for the much more effective N95 respirators. I even for a time sewed a number of cloth masks from the HK Mask site pattern. Much of this was based on research showing that surgical masks could reduce influenza transmission, and even homemade masks could be of some help in reducing disease spread.

Without getting too much into the weeds, it's useful to pause a moment and describe what it is we're trying to measure and do. Slate Star Codex in March ran a very good summary of the scientific literature regarding mask-wearing and why one might or might not choose to wear masks. The first order of business is defining how transmission occurs:

Epidemiologists used to sort disease transmission into three categories: contact, droplet, and airborne. Contact means you only get a disease by touching a victim. This could be literally touching them, or a euphemism for very explicit contact like kissing or sex. Droplet means you get a disease when a victim expels disease-laden particles into your face, usually through coughing, sneezing, or talking. Airborne means you get a disease because it floats in the air and you breathe it in. Transmission via “fomites”, objects like doorknobs and tables that a victim has touched and left their germs on, is a bonus transmission route that can accompany any of these other methods.

More recently, scientists have realized that droplet and airborne transmission exist along more of a spectrum. Droplets can stay in the air for more or less time, and spread through more or less volume of space before settling on the ground. The term for this new droplet-airborne spectrum idea is “aerosol transmission”. Diseases with aerosol transmission may be spread primarily through droplets, but can get inhaled along with the air too. This concept is controversial, with different authorities having different opinions over which viruses can be aerosolized. It looks like most people now believe aerosol transmission is real and applicable to conditions like influenza, SARS, and coronavirus.

Sifting through the papers, Scott Alexander writes,

I think the evidence above suggests masks can be helpful. Masked health care workers were less likely to catch disease than unmasked ones. Masked travelers on planes were less likely to catch disease than unmasked ones. In per protocol analysis, masked family members are less likely to catch disease from an index patient than unmasked ones. Laboratory studies confirm that masks block most particles. All of this accords with a common-sense understanding of droplet and aerosol transmission of disease.

And that's where I was as of March.

And then came the Osterholm Update podcast of June 3 about masks (transcript here).

Never before in my 45 year career have I seen such a far-reaching public recommendation issued by any governmental agency without a single source of data or information to support it. This is an extremely worrisome precedent of implementing policies not based on science-based data or why they were issued without such data. ...

... When people state that CDC recommends cloth face mask use you have to understand there was much more going on than science and public health protection with this recommendation. I urge you go online to the CDC website yourself and you’ll not find one piece of information supporting that cloth masks are effective in reducing respiratory virus transmission.

Osterholm flat out accuses the CDC's stance change coming, in part, from arm twisting. ("Well, I signed [the MASKS4ALL open letter recommending public mask wearing] because of pressure from peers"). There's a great deal more there, which I recommend everyone read or listen to. I find him persuasive on the state of ignorance we live in regarding the efficacy of masks (and how much they can help in situations likely to transmit infection), but I will continue to wear masks in public and recommend others do as well.