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Colby Cosh: Here's the latest good reason to wear a face mask

The most interesting COVID-19 item of last week might have been an editorial, as opposed to a piece of formal research, which appeared in the New England Journal of Medicine Sept. 8 . It’s another sign that we are entering a new phase of the COVID war: after a season in which hospitals were bracing for cataclysm, and scientists were scrambling to perform trials of literally any reasonable-sounding treatment, doctors are beginning to step back and seek a broader view of the struggle.

In their introduction, epidemiologists Monica Gandhi and George Rutherford of the University of California San Francisco discuss the delayed arrival of masks as an acceptable way of controlling the novel coronavirus SARS-CoV-2. In their account, public health doctors knew or ought to have known that masking in public places might help prevent viral spread, as it does in clinic settings and surgeries. But this question didn’t become urgent until global medicine realized that asymptomatic carriers of the virus were shedding infectious particles as aggressively as the ill, or more so.

Looking back, there is obviously something to this. Spread by asymptomatic persons was initially assumed, on the basis of experience with historic viral diseases, to be a trivial consideration in fighting COVID. This was, for example, one premise of the still-contested Swedish approach. But Sweden, like almost everywhere else, is still having new cases. The original dogma that asymptomatic spread is rare, and can be disregarded, has become difficult if not impossible to believe.

Sweden, like almost everywhere else, is still having new cases

That’s the bad news: SARS-CoV-2 is by nature more difficult to eradicate in any population by checking people for symptoms (although Canada wasn’t well equipped to even do that much) and applying quarantine measures on that basis. The good news, Gandhi and Rutherford suggest, is that we may have underestimated the power of masks because of science’s habit of binary thinking.

Citizens are being urged to wear masks by the authorities on the premise that masks will reduce your probability of becoming infected. If you and the COVID-positive person near you are masked, or if one of you is, there is less chance of you flipping from the epidemiologist’s “susceptible” (S) category to the “infected” bin (I). But it’s probably not quite that simple. Masks, the UCSF pair suggests, may also be limiting the payload of viral particles that reach the tissues of Mr. Infected — the “inoculum,” in technical language, of the virus.

The authors note that there is an alternative tradition in virology that speaks of the “LD-50” of a virus. You may have heard of the LD-50 concept in toxicology: it’s the amount of a particular poison, usually scaled to body mass, that will kill half of those who are exposed to it. The dose, as they say, makes the poison. We now know that viruses are not literal poisons, despite their Latin name, but viral diseases might be dependent on “dose” in an analogous way. Some viruses probably have their own unmeasured LD-50, and there is indirect evidence that SARS-CoV-2 behaves this way.

Direct measurements of the phenomenon are hard to find, but the NEJM paper cites a Japanese-led study which found that “higher doses of administered virus led to more severe manifestations of COVID-19 in a Syrian hamster model of SARS-CoV-2 infection.” They didn’t put teeny-tiny little masks on the hamsters, if you’re wondering, which I definitely was. The Japanese study doesn’t actually mention masks, and animal models have to be taken with a grain of salt anyhow.

But the ratio of asymptomatic infections to symptomatic ones (in humans) appears to be higher in health-care settings where the personnel are always masked. Countries with high masking compliance are having lower rates of severe COVID-19 and death. And Gandhi and Rutherford don’t mention it, but the hospital burden per infection seems to be declining in such countries as Canada that adopted mask policies late and are bracing for a “second wave” of spread.

We may find, the authors suggest, that we have all been engaging in a mass program of “mask variolation.” Variolation is the name now given to the original method of vaccination — collecting fluids from smallpox patients (who carry the variola virus) and exposing the well to small amounts of diseased matter in order to induce a very mild infection that provides immunity.

We may find that we have all been engaging in a mass program of ‘mask variolation’

That could be what masks are doing for humans — reducing the chance of infection, as we have been told explicitly, but also making the infections that do happen less serious, and immunizing transit riders or bodega shoppers who may never be the wiser. The permanence of any immunity remains to be seen, but in this regard it seems that SARS-CoV-2 does, fortunately, act like its precursors.

It’s a hypothesis crying out for tests, and the NEJM editorial implicitly suggests a check of the rates of asymptomatic infection before and after the introduction of mask guidelines. Canada, having a chronic national case of data constipation, is not the place for this to be done; probably it requires longitudinal study of a particular population.

It has become somewhat difficult to talk about masks objectively at all since they were turned into a symbol of creeping authoritarianism by political opportunists and social-media provocateurs. Public health officials are wearing a lot of invisible armour now when they go before the cameras, and “mask variolation” isn’t ready for prime time as an established scientific fact to be explained in simple Anglo-Saxon words. I guess that’s what newspaper columns are for.

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