Masks Aren’t Enough to Stop COVID-19 Spread Without Distancing, Physics Proves

It took physicists to test how well mask materials block droplets. The common ones block almost all – but in close proximity to a sick person, you can still catch it

Ruth Schuster
Ruth Schuster
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People wearing protective masks walk in the departure terminal of Cointrin airport, Geneva, December 21, 2020.
People wearing masks and distancing at the departure terminal of Cointrin airport, Geneva, December 21, 2020. Credit: DENIS BALIBOUSE/REUTERS
Ruth Schuster
Ruth Schuster

Wearing a mask is crucial during a pandemic caused by a virus that can spread through the air. But it’s not enough. Social distancing is crucial too, physicists reported on Tuesday. The best preventative is masking up and socially distancing, always.

Krishna Kota of New Mexico State University and colleagues tested the efficacy of five different mask materials in preventing the spread of SARS-CoV-2 virus particles in droplets that we shoot out by cough or sneeze. The results were published in the journal Physics of Fluids.

Infection is a function, among other things, of the number of viral particles to which a person is exposed. All five mask materials dramatically reduced the number of droplets that were spread, the researchers found. But at distances closer than 2 meters (6 feet, 7 inches) – which is the social distancing norm in Israel – enough droplets made it through some of the materials to potentially cause illness.

“A mask definitely helps, but if the people are very close to each other, there is still a chance of spreading or contracting the virus,” Kota stated. “It’s not just masks that will help. It’s both the masks and distancing.”

The mask materials were tested using a machine that blows air laden with liquid particles, mimicking natural viral-laden coughs and sneezes, down a tube. The tube was blocked by the mask materials, to wit: a regular cloth mask; a two-layer cloth mask; a wet two-layer cloth mask; a surgical mask; and a medical-grade N95 mask.

Statistically, they say, the N95 mask stopped 100 percent of the droplets. (This paper did not cover other considerations when choosing one’s mask.) The others captured almost all the laden droplets – though the cloth mask still enabled about 3.6 percent of the droplets to pass.

The test apparatusCredit: Javed Akhtar

The thing is, at a close distance and given a bit of time, that could suffice to infect. Infection is a function of proximity and time as well as susceptibility, among other things. The higher a person’s viral load, the more particles they will disseminate when they cough, sneeze or even talk, but it can reach hundreds of millions of viral particles per sneeze.

How many viral particles you need to breathe in (or catch through your eyes) to get infected depends on multiple factors, including your state of health, but we don’t have a figure yet. The amount of virus necessary to cause illness is called the “infectious dose” and we don’t know it for the coronavirus, let alone for the new mutant strain plaguing southern England, which is reportedly 70 percent more infectious than the original strain. The infectious dose for the coronavirus is suspected to be quite low, and the dose of that mutant strain would be much lower.

Max Planck helpfully published a calculator for aerosol infection risk in a closed environment i.e., indoors, but it doesn’t consider close proximity to a sick person, in which case the probability is off the charts.

“A single sneeze can carry up to 200 million tiny virus particles, depending on how sick the carrier is. Even if a mask blocks a huge percentage of those particles, enough could escape to get someone sick if that person is close to the carrier. Without a face mask, it is almost certain that many foreign droplets will transfer to the susceptible person,” Kota said.

We add here that more and more animals from dogs and cats to hamsters are catching the coronavirus from us; whether they can then infect humans remains uncertain.

It bears adding that masking up your Adam’s apple or chin is no help whatsoever. Neither is wearing it over your mouth but leaving your nose exposed. These are categorically exercises in futility. Exercising in the open is no excuse not to mask up in public. Also, if you’re using homemade masks, fine, but wear once and wash.

Yes, it’s becoming tedious, and familiarity tends to breed contempt. You may figure if you didn’t get it yet, you “probably” won’t, and who can stand all this distancing anyway? But with all due respect to the vaccines, it isn’t over.

This paper proves that we need to keep wearing masks and maintaining social distancing, including at the supermarket. It is arguably not worth paying for a lost place in a cashier’s line with your life.

Volunteers wearing face masks wave after they load boxes onto a delivery truck during an event to send Christmas gifts for the underprivileged in Seoul, South Korea, December 22, 2020.Credit: Lee Jin-man/AP

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