Scientific evidence supports the use of face masks to reduce COVID-19 spread, mainly by preventing infectious liquid particles from reaching uninfected people

An article published on 6 April 2021 by Townhall Media, authored by radio talk show host Dennis Prager, claimed that mask-wearing is unsupported by science. Prager’s article received more than 14,000 interactions on Facebook, according to social media analytics tool CrowdTangle.

In the article, Prager claimed that “If you wear a mask, you do so in the belief that you are protecting yourself (and others) from COVID-19”. Based on this premise, he questioned why mask-wearers would be concerned about other people around them not wearing a mask, saying “Doesn’t your mask protect you?”

This line of questioning is misleading, as it wrongly assumes that the primary reason people wear cloth face masks is to protect themselves. In fact, the U.S. Centers for Disease Control and Prevention (CDC) and other health authorities explain that mask-wearing is primarily a means of blocking potentially infectious liquid particles from being disseminated in the air. According to the World Health Organization (WHO), evidence indicates that the main mode of COVID-19 transmission is through infectious liquid particles, which are released into the air when an infected person coughs, sneezes, talks, or sings.

The CDC states that “Masks are a simple barrier to help prevent your respiratory droplets from reaching others. Studies show that masks reduce the spray of droplets when worn over the nose and mouth”. In other words, the main purpose of wearing cloth face masks isn’t for personal protection, as Prager’s question implied, but to protect the people around the wearer.

The CDC published a list of scientific studies providing data that support community use of masks on this webpage, summarised thus:

“Multi-layer cloth masks block release of exhaled respiratory particles into the environment, along with the microorganisms these particles carry. Cloth masks not only effectively block most large droplets (i.e., 20-30 microns and larger) but they can also block the exhalation of fine droplets and particles (also often referred to as aerosols) smaller than 10 microns; which increase in number with the volume of speech and specific types of phonation. Multi-layer cloth masks can both block up to 50-70% of these fine droplets and particles and limit the forward spread of those that are not captured. Upwards of 80% blockage has been achieved in human experiments that have measured blocking of all respiratory droplets, with cloth masks in some studies performing on par with surgical masks as barriers for source control.”

Prager also claimed that wearing masks outdoors is “foolishness”. He offered no evidence to support his claim, instead citing “common sense”.

While health authorities like the CDC state that the risk of COVID-19 transmission is lower outdoors as compared to indoors, there are several caveats to this, such as the amount of time that people interact with each other and the physical distance between people.

For instance, a runner who passes someone for a brief interval of time poses little risk of infecting others, as several scientists explained in this article by Deutsche Welle, a German public broadcaster. However, scientists pointed out that if people are in close contact with one another over prolonged periods of time, like during a concert, then wearing face masks is a “sensible” idea.

Experts who were interviewed in this CTV News article also came to the same conclusion. In the article, Anna Banerji, director of global and indigenous health at the University of Toronto, said, “The risks for outdoor transmission are generally low, but it depends on context. If you are sitting with the same person for a while the risks increase, versus passing someone by on the street”.

A National Geographic article published on 9 April 2021 that also discussed the question of outdoor mask-wearing, highlighted the same points. Saskia Popescu, an epidemiologist and adjunct professor at the University of Arizona in Phoenix, explained:

“The three key factors to consider are distance, duration, and intensity, she says. The closer people are, the more droplets an activity is generating, and the longer people are close to one another, the more the risk increases and the more important a mask becomes. As with so much else in the pandemic, infection risk—and the need to wear a mask—hinges on the context.”

Prager claimed that “There are plenty of experts with evidence-based views to the contrary”, going on to quote Anthony Fauci, director of the U.S. National Institute for Allergy and Infectious Diseases, who said during a 60 Minutes interview on 8 March 2020 that “There’s no reason to be wearing a mask”.

The use of this quote is misleading, as Fauci made the statement before evidence emerged that people who don’t show symptoms of COVID-19 can also spread the virus^[1-3]. When the interview was conducted, health authorities discouraged the public from wearing face masks due to extreme shortages of surgical and N95 masks, which were needed to protect healthcare workers.

The discovery that seemingly healthy people could spread the virus led public health authorities like the WHO and the CDC to reverse their stance on face masks, recommending that members of the general public wear face masks, even if they feel well.

This isn’t the first time that outdated guidance on face masks discouraging their use was cited as if it was still current; the practice began as far back as July 2020, as documented in this Health Feedback review. As Reuters pointed out in their fact-check, Fauci has since encouraged mask-wearing numerous times in the media (see here, here, and here).

Next, Prager quoted other physicians and scientists who claimed that masks don’t work or are dangerous. However, scientific evidence doesn’t support their claims. Several published studies reported that mask-wearing can reduce the spread of viral respiratory infections like COVID-19.

An April 2020 study published in Nature Medicine, examined how more than 100 people shed various respiratory viruses, including seasonal coronaviruses and influenza, as well as the efficacy of face masks in reducing dissemination of infectious droplets^[4]. The authors found that surgical masks reduced the detection of coronavirus and viral copies in large respiratory droplets and aerosols, suggesting that masks can reduce viral transmission.

An April 2020 review published in the International Journal of Nursing Studies by MacIntyre and Chughtai analyzed 19 randomized controlled trials, among which eight were conducted in a community setting^[5]. The review concluded that, “In the community, masks appear to be effective with and without hand hygiene, and both together are more protective.”

A May 2020 study published in BMJ Global Health measured the incidence of secondary COVID-19 transmission in 124 families in Beijing, China. Each family had one member with a confirmed COVID-19 infection (primary case). The authors examined whether various interventions, specifically the use of disinfectants, physical distancing, and face masks, in a household reduced the risk of secondary transmission^[6]. They found that all three interventions reduced secondary transmission of COVID-19. In particular, the authors noted that “Face mask use by the primary case and family contacts before the primary case developed symptoms was 79% effective in reducing transmission.”

A systematic review and meta-analysis by Chu et al., published in June 2020 The Lancet, examined the efficacy of three interventions—physical distancing, face masks, and eye protection—in reducing the transmission of coronavirus infections (SARS, MERS, and COVID-19)^[7]. The authors evaluated 39 studies testing the efficacy of various face masks in reducing disease transmission and found that face masks reduced the risk of coronavirus infection compared to no mask wearing.

An article published in the Proceedings of the National Academy of Sciences of the United States of America in January 2021 reviewed the evidence supporting the use of face masks, particularly as source control. The authors evaluated a diverse array of studies that examined epidemiological evidence, transmission characteristics of respiratory viruses, and filtration capacities of face masks^[8]. They concluded that:

“The available evidence suggests that near-universal adoption of nonmedical masks when out in public, in combination with complementary public health measures, could successfully reduce [the effective reproduction number] to below 1, thereby reducing community spread if such measures are sustained.”

Prager then wrote that the Wall Street Journal reported on 11 November 2020 that “The projected number of lives saved, and the implied case for a mask mandate, are based on a faulty statistic”. This quote comes from an opinion piece written by economic historian Phillip Magness about a study published in Nature Medicine in October 2020.

Magness’ article centered on an outdated figure that was used in the study to model the spread of COVID-19 and predict the COVID-19 death toll^[9]. The figure underestimated the proportion of Americans who wear face masks. In a statement to the blog Retraction Watch, the group that conducted the study, the Institute for Health Metrics and Evaluation (IHME) at the University of Washington, acknowledged that their figure was outdated and an underestimate.

As Retraction Watch explained, the outdated figure resulted in an overestimate of the predicted number of lives that would be saved with mask mandates:

“That would mean the difference between current mask use and 95% would be much lower, and the additional benefit of near-universal mask wearing — while still substantial — would mean fewer than 130,000 lives saved.”

Magness’ article highlighted that implementing mask mandates wouldn’t save as many lives as reported in the IHME study. But this isn’t the same as saying that “masks are essentially useless”. The IHME revised its estimate of the number of lives saved from 130,000 to 63,000, which is still a substantial number of lives saved.

Finally, Prager cited a quote that he claimed was from a study published in the New England Journal of Medicine, regarding the efficacy of face masks during “a passing interaction in a public space”.

His use of the quote in this context is inaccurate and misleading. Firstly, the quote comes from a Perspective article published in the journal, which commented on research findings by others, but didn’t report research of its own. Therefore, it is inaccurate to call it a “study”.

Secondly, the authors clearly encouraged widespread mask-wearing in their Perspective article:

“Expanded masking protocols’ greatest contribution may be to reduce the transmission of anxiety, over and above whatever role they may play in reducing transmission of Covid-19. The potential value of universal masking in giving health care workers the confidence to absorb and implement the more foundational infection-prevention practices described above may be its greatest contribution.”

But Prager cherry-picked one passage of the article to imply that the authors shared his opinion on masks. In a follow-up article also published in the same journal, the authors went on record to state that the intention of their article was to encourage mask-wearing, which refutes Prager’s claim:

“We understand that some people are citing our Perspective article (published on April 1 at NEJM.org) as support for discrediting widespread masking. In truth, the intent of our article was to push for more masking, not less. It is apparent that many people with SARS-CoV-2 infection are asymptomatic or presymptomatic yet highly contagious and that these people account for a substantial fraction of all transmissions. Universal masking helps to prevent such people from spreading virus-laden secretions, whether they recognize that they are infected or not.”

Overall, the claim that mask-wearing is a practice unsupported by scientific evidence is false. On the contrary, several published studies support community mask use as an effective means of reducing the spread of viral respiratory infections like COVID-19. The opinion piece also misleads readers by quoting outdated guidance and misrepresenting statements made by others to give the inaccurate impression that Prager’s claim is scientifically supported, when the opposite is true.

REFERENCES

• 1 – Kimball et al. (2020) Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020. Morbidity and Mortality Weekly Report.
• 2 – Wei et al. (2020) Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020. Morbidity and Mortality Weekly Report.
• 3 – Li et al. (2020) Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2). Science.
• 4 – Leung et al. (2020) Respiratory virus shedding in exhaled breath and efficacy of face masks. Nature Medicine.
• 5 – MacIntyre and Chughtai. (2020) A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients. International Journal of Nursing Studies.
• 6 – Wang et al. (2020) Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China. BMJ Global Health.
• 7 – Chu et al. (2020) Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. The Lancet.
• 8 – Howard et al. (2021) An evidence review of face masks against COVID-19. Proceedings of the National Academy of Sciences of the United States of America..
• 9 – IHME COVID-19 Forecasting Team. (2021) Modeling COVID-19 scenarios for the United States. Nature Medicine.