Can Masks Function as a Crude Vaccine?

A new theory suggests masks lead to less severe infections that still offer immunity

There is mounting evidence to suggest that masks are effective at protecting people from Covid-19 both by limiting the chance someone comes into contact with the virus and by reducing the severity of the disease if they do get infected. A new opinion paper published this week in the New England Journal of Medicine takes the power of masks one step further, suggesting they could serve as a sort of crude vaccine — historically known as “variolation” — for the novel coronavirus. The idea is that masks expose people to just enough virus to cause them to develop an immune response to it but not enough to get sick.

The Medium Coronavirus Blog spoke with one of the paper’s authors, Monica Gandhi, MD, MPH, a professor of medicine at the University of California, San Francisco, about the benefits and drawbacks of the idea, which types of masks are best, and why the U.S. doesn’t have a mask mandate. The interview has been lightly edited for length and clarity.

Medium: I’m fascinated by this idea of masks as a sort of variolation, or a stop-gap for a vaccine. I’d love to hear how you came up with this theory.

Monica Gandhi: I’ve been really interested in how much asymptomatic infection there is with Covid-19. It’s very different from other respiratory viruses, or any other virus, where you can get totally sick or you can be completely fine. So I was trying to understand the risk factors for asymptomatic infection, and we started noticing that in any setting where masking was done, there’d be a lot of asymptomatic infection. In cruise ships, food processing plants — people got sick, they started masking, they didn’t get sick anymore. It really seemed to drive up the rate of asymptomatic infection from 40% as a standard to 81% on a cruise ship, 95% in jails, and 95% in food processing plants when they started giving masks routinely.

In our article in the Journal of General Internal Medicine that came out three or four weeks ago, we tried to put together all the evidence for why that would be. And, essentially, masks reduce your viral inoculum [the amount of virus a person is exposed to]. It’s very well known in science that the lower viral inoculum you get, the less sick you get. So putting it all together, it seems like masks increase rates of asymptomatic infection [by decreasing viral inoculum].

Then, over the last month, we’ve been getting these amazing studies about asymptomatic infection leading to really strong T-cell immunity. This isn’t shocking because it’s actually probably the process by which you get asymptomatic infections — the lower viral inoculum allows you to have a really strong and organized adaptive immune response. And we’ve been seeing cases go up in places that have opened up, like San Francisco, but the case fatality rate has been so low in cities that mask compliantly. So are we actually getting immunity by getting cases with our masks but not getting fatalities?

How does variolation fit into all this? What does that mean?

This is a theory [that originated with smallpox]. They would have these parties where they would cut their arm and put inside a piece of hair, a scab, some pus, anything from an individual infected with smallpox. The idea was that you would give people small amounts of virus — by definition, that’s what variolation is — and hope that you’d get an asymptomatic or mild infection and then hope that you could generate immunity, which it absolutely did. In fact, that’s what led to the concept of vaccination with bits of virus. Variolation really launched vaccine development.

Masking also seems to decrease the severity of disease, and then if that’s going to lead to immunity to boot, that’s what we mean by masking being a kind of variolation, or a poor man’s vaccine.

How do masks compare to a vaccine in terms of long-term immunity? Is there some world where if a vaccine takes too long, we could actually reach herd immunity through mask variolation?

That fundamental question of “What does natural infection do for you in terms of durability of immunity versus vaccine generated immunity?” is unclear for SARS-CoV-2. We do know, for example, that with chickenpox and DNA viruses, natural infection is durable immunity, meaning usually people don’t get chickenpox twice. We know with measles, which is an RNA virus like SARS-CoV-2, that people got pretty long-lasting immunity from natural infections but sometimes could get it again. And, by the way, same thing with the vaccine; that’s why we get multiple booster shots of the vaccine as children. But the duration of immunity from natural infection versus what we’re going to get from a vaccine is unclear with SARS-CoV-2.

With some other coronaviruses, there has been super hopeful data that getting lots of colds, for example, does generate long-lasting T-cell responses. That’s the other potential explanation behind asymptomatic infection—we have these cross-reactive T-cells to other coronaviruses. So it’s a hopeful sign from other coronaviruses, including SARS-1, that natural infection can give you durable immunity. But we don’t know yet with this virus. One thing is that we see antibodies coming down faster with asymptomatic SARS-CoV-2 than we do with severe infection. I think that’s not that depressing, though, because durable immunity with viruses is mediated by memory T-cells and memory B-cells, not antibodies. So, I would say, we don’t know, but I think it’s really hopeful.

Is there a concern with the asymptomatic spread that you could be infecting people in your own household? Would this require people to wear masks inside the home at all times? Because if you’re infected asymptomatically and have no idea that you have the virus, you’re still shedding tons of virus and so could infect someone in your home who then has a full-blown infection.

Yeah, inside the home, where we have not recommended masking, is quite an area of debate. I have two young children who I’m desperately waiting to go back to school, and I have two older parents who are 86. And if my parents lived with me, I’d probably have my children masked or them masked. So yes, I do think that there is a degree of vulnerability in the home. If someone already has host defenses down because of their age or another risk factor — cardiovascular disease, obesity — then I would consider masking in that situation.

Would the masks be able to protect enough against airborne spread? Most people don’t have N95 masks, they have cloth masks, so would they still block enough of the infection for this to work?

The mask literature is not convincing that you need to block out all viral particles by having a tight-fitting N95 mask to protect you from airborne spread. It’s true that N95 masks, because they’re tight-fitting and because their fibers are really close, probably block out the majority of viral particles, whereas cloth and surgical masks — two-ply when I say cloth — block out about 85%. That’s literature from other respiratory viruses, not SARS-CoV-2, because [you can’t do the experiments you’d need to do] where you spray people with virus because it’s obviously not ethical. But there was a hamster mask study from Hong Kong that got a lot of attention and showed that transmission was decreased quite a bit when you simulated masking the hamsters, and even if they got infected, which some of them did, they had mild infections. So you may not need to block out all the virus.

A follow-up question to that, would wearing two masks help? Is there any additional benefit of wearing a cloth mask and a surgical mask rather than just one or the other, or would that largely be superfluous?

I think it’s superfluous. Research with other respiratory viruses shows that a two-ply cloth face mask blocks out as much as a surgical mask. I would just advise two-ply masking, covering nose and mouth, of course.

This is more of a policy question, but why don’t we have a universal mask mandate yet? Is it purely political? Is there any doubt about how well they work?

I think there is very little doubt that they work. So why don’t we have a national mask mandate, which I believe we should? I think it is entirely political. We have a president who doesn’t model masking. We have a Libertarian streak in this country that makes it seem like we’re restricting people’s freedom — which is exactly what happened when we mandated seat belts to limit car crash fatalities, by the way. And I think we did some wrong messaging at the beginning. The messaging in April from the CDC was “Wear a mask to protect others.” We are not a civic-minded nation at the moment. I think we need to stress that it does protect you as well as others.

My last question for you is a little bit sticky. Are you worried that people will try and get infected with SARS-CoV-2, like the pox parties that you mentioned, or even chickenpox parties more recently? Is that a concern? And is there a way someone could do it right, or is that just a road we don’t want to go down?

Yeah, I was worried that this could be misperceived as this article saying that. I definitely wouldn’t encourage pox parties, and I don’t think that people should deliberately be infected. I did try to put a lot of caveats in the article that said that. So yeah, I’m worried that it could be misperceived, but I hope the article is worded carefully enough that it won’t be. I hope people don’t misunderstand that it’s saying I want them to get infected because it’s not. I want people to be safe.