Two Masks are Better Than One

In these COVID times
It is so hard to mask up
Without losing face

Masks and COVID-19. Hasn’t this topic been exhausted yet?

Amazingly, we continue to learn more about masks and their role in the current pandemic. One would think that there wouldn’t be that much to say about something as simple as a mask that’s been in everyday use in operating rooms for 150 years. And masks have been a tool used to combat viral pandemics for the last 100 years; masking played a central role in reducing the carnage of the Spanish Flu of 1918.

So, we might expect that masks would be pretty well understood by now. But science is tricky that way; there’s almost always more to the story.

Evidence is now overwhelming that masks reduce the amount of virus broadcast by people shedding virus, and thus protect everyone near a person who is ill but wearing a mask. Careful measurements of virus escaping from humans ill with a coronavirus similar to COVID-19 found that masks completely blocked detectable virus (Leung et al., Nature Med. 5/2020).

Although it would be unethical to intentionally expose humans to COVID-19, as luck would have it hamsters are susceptible to this virus. This happy circumstance (for us, the hamsters not so much) allowed Yuen Kwok-yung (Clinical Infectious Diseases, May 2020) to infect one cage of hamsters with COVID-19 and test the transmission rate to an adjacent cage when a sheet of mask material separated the two cages. The mask material reduced infection transmission four-fold, showing that masks can make a big difference.

Very recent paper by Gandhi et al in the Journal of General Internal Medicine (August, 2020; not yet peer reviewed) makes a convincing case that masks also benefit the wearer. Gandhi’s argument hinges on the fact that with COVID-19, as with all infectious diseases, dose matters. We don’t yet know the minimum number of COVID-19 virus particles necessary to infect a human, but it’s likely between hundreds and thousands. So, anything that reduces the number of viral particles to which someone is exposed will reduce the risk of becoming ill. Moreover, even if illness does occur, reducing the inoculum of viral particles makes the subsequent illness less severe. Is this really true? Well, our friends the hamsters who were protected by the mask partition not only were less likely to fall ill with COVID-19, but those hamsters who did become ill had milder cases of COVID-19.

Gandhi also presents an “experiment of nature” in which he compares the results of COVID-19 outbreaks on two cruise ships: on one ship out of Argentina which provided masks to passengers and crew, while on the second cruise ship (Diamond Princess) no masks were available. In the ship where masks were used while just over half of patients eventually tested positive, most (81%) of such patients were asymptomatic; on the diamond princess, by contrast, only 20% of COVID-19 cases were asymptomatic. The clear implication is that the severity of COVID-19 was reduced in passengers who were able to wear masks, and often reduced a lot, all the way down to asymptomatic. A similar dynamic has been seen in other close quartered populations (Hair salons, chicken processing plants, etc.) where those wearing masks were more likely to develop asymptomatic COVID-19 infections, again presumably because of reduced viral inoculum.

Gandhi also notes that the decreasing COVID-19 mortality rates in the wake of increasing mask rates suggests that masks may be at least in part responsible for better overall survival rates. Yes, physicians are getting better at treating COVID-19, but the increase in asymptomatic case suggests that reducing the viral loads that people are exposed to lessens their risk of serious disease, easing the task of physicians in caring for COVID-19 patients.

But, sometimes the best way to tell a story is to tell a story. So here are two: On January 23 a person ill with COVID-19 went to a crowed restaurant in Guangzhou with several friends for a two-hour lunch. No one wore masks and within days 10 people sitting close to the shedder developed the disease (Lu et al. Emerging Infectious Disease, July 2020). On the same day a traveler with COVID-9 and a dry cough boarded an airplane in in Wuhan along with 350 other travelers for the 14-hour flight to Toronto. Fortunately, he was wearing a mask, and none of his fellow passengers developed COVID-19 (Schwartz, CMAJ, 4/14/2020). These are just two case reports, of course, but together they tell a compelling tale: masks work.

Mask Math: The real strength of universal masking is simply that if everyone wears a mask a virus must penetrate not one but two masks to cause mischief. And the mathematics of masking is against the virus, because the effect of two masks isn’t added together; it’s multiplied. So, if a person shedding COVID-19 is wearing a mask that allows 1% percent of viral particles through, and a non-infected person’s mask allows 1% of viral particles through, overall only 0.01% of viral particles make it to the non-infected person. And remember, the goal isn’t to block every single viral particle, but only to drop the number of viral particles lower than the infective dose; so if a few hundred or a few thousand of viral particles make it through the two masks, disease won’t be transmitted.

So masks: cheap, no side effects, and by far our most effective defense against COVID-19. And now they come in attractive colors and interesting patterns. How can we not love them? Or, at least, learn to love them?

In view of all this the rise in “mask haters” seems puzzling. Yes, at first there were missteps in messaging by public health authorities who initially claimed only health care providers needed masks. This was unfortunate, and untrue, but has since been reversed. Perhaps more significantly, masks were seized upon as flags of tribal affiliation rather than tools of pandemic control, and this has proven much harder to walk back, perhaps because it is so difficult to change political positions.

The ease with which information, and especially misinformation, flows over the internet has worsened this problem. One can easily find articles on the web such as “Masks Likely Do Not Inhibit Viral Spread” which feels like clickbait. And is: the 22-page transcript provides no support for the title of the article. Rather, it seems an entrepreneurial osteopath selling nutritional products is using this article to attract people with a nonstandard approach to their health care to his online store in hopes of selling expensive dietary supplements.

No every article on the web is there to inform; more often the goal is to manipulate and monetize. It’s not easy to give a single rule of thumb that will reliably distinguish between reliable research and conspiracy theories. But if something seems not to make sense, well, maybe it’s because it doesn’t. (ow could a mask hurt anyone? How could containing sneezes with a mask not reduce transmission of a respiratory virus? And it’s important to check the source of a message. It’s hard to assess the motivation of most writers one encounters on the web. But Dr. Anthony Fauci is a guy we’ve know for decades through other pandemics, and we pay his salary. We can be pretty sure he’s telling us the truth as he understands it, and that he has our interests at heart. Other sources, well, it’s not easy to figure out.

If everyone wore masks it’s likely that the R0 of COVID-19 would drop below 1. The virus would then recede across the country, buying us time for a vaccine. The fact that this simple, safe, and effective measure has been late in its deployment and spotty in its adoption has already cost tens of thousands of lives. It’s literally heartbreaking for many families.

But if word gets around that wearing a mask is not just in your neighbors’ interest but also makes you less likely to contract COVID-19, well, maybe the popularity of masks will finally take off. Spread the word: Masks keep others safe, and improve your personal chances of living COVID-19 free to a ripe old age. Finally, some good news about the pandemic.

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