Speaking of Science: Viruses and masks

Speaking of Science: Viruses and masks

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I recently moved to Bethesda, MD to start work at the National Institutes of Health. It is very muggy here with humidity well into the 80-90% range. After it rains, you can see the steam billowing from the sidewalk and condensing on buildings and street posts. All of this makes it rather uncomfortable walking around with a mask on, trapping moisture from my breath in the humid air against the entire lower half of my face. You might reasonably ask why I’m choosing to wear a mask if it’s so uncomfortable. The obvious answer is to stop the spread of sars-CoV-2, the virus causing Covid-19 around the globe. But I know many people are hesitant to wear a mask or wonder if it can actually work.

Even though I work at the NIH, I don’t spend much time thinking about viruses or masks; neither is something I study regularly. So I decided to devote some time into looking into the research on masks, viruses, and especially sars-CoV-2 to answer some of the most common questions I’ve heard from people, or thought myself.

Question 1: Aren’t viruses small enough to go right through cloth or even surgical masks? If so, how can a mask help prevent spreading a virus?

Viruses are usually in the range of a few hundred nanometers (nm) which is indeed very small (a one foot long ruler is 305 million nm). N95 masks, which are widely considered the best at protecting the wearer from bacteria and viruses, still only filter out 95% of particles on the 300 nm level, which is only slightly larger than most viruses. Cloth and surgical masks likely only filter out even larger particles. So, while it might seem that viruses will go straight through masks, there is more to it than that it turns out. Most viruses, including Sars-CoV-2, are spread in liquid droplets released not only when you cough and sneeze, but also when you speak. This is important because droplets are much larger than an individual virus. When droplets are expelled from your mouth or nose, they can be halted almost entirely by a fabric mask, tissue, or some other plastic barrier like a face shield. A study from Nature Medicine analyzed the breath from people sick with influenza or seasonal coronaviruses (related to Sars-CoV-2) when breathing either into open air or through a mask. They found that even disposable surgical masks greatly reduce the number of viruses expelled into breath beyond the mask. So, while it’s possible some viruses can still make it through cloth or surgical masks, cloth masks will block out many of them, and slow down the remaining viruses that make it through so they can’t spread as far.

Question 2: Why did policy on masks change? Does this mean scientists don’t actually know if they work?

The answer to this is simple: science, and by extension medicine, are evidence driven pursuits. No two viruses are the same in terms of how they are spread, how long they can stay on a surface and still infect you later, and how they enter the body. Sars-CoV-2 is an entirely new virus that has only existed since around December. As we learn more about the virus, answers change. Scientists initially felt that having healthy appearing people wear masks might lead to shortages for front line medical workers and infected individuals (remember what happened with the TP hoarding…). But once it became clear a healthy-appearing person can in fact be sick with Sars-CoV-2 and actively spreading the virus, the only thing to do was accept this new evidence and recommend masks for everyone.

Question 3: Why do officials keep saying masks protect the people around you, but not the person wearing the mask? If my mask can protect people around me, how can it not be protecting me?

The reason for this isn’t that masks are somehow ineffective- it’s actually based on the shape of the mask and the way viruses mostly spread through droplets when you cough and sneeze. You might have noticed that cloth masks and surgical masks don’t fit perfectly; they tend to have some room around the edges or even below them. That means that while the viruses you exhale in droplets will smash into the mask right in front of you, if someone coughs into the open air, the virus can spread through the air and in theory slip through the holes in the sides or bottom of your mask to infect you. This is why masks are most effective if everyone is wearing them, especially since you can spread Sars-CoV-2 without displaying symptoms. A few studies already suggest this method actually works. For instance, The BMJ found in May that in households in China where everyone wore facemasks even before knowing someone was sick, transmission was cut by 79%.

Question 4: So, can masks actually help?

It seems so. Numerous studies, including computational modeling of infection levels around the globe, observational studies of infected individuals, and direct tests on how viruses spread through masks all seem to point to the same thing: wearing masks greatly reduces the spread of Sars-CoV-2. Until there is scientific evidence that we have a better protective measure or treatment, limiting virus spread, even if it isn’t perfect or 100% effective all the time, seems like a very good thing to do if the only price is a bit of discomfort from a face covering.

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