Over 400 Studies Show Face Masks Protect Against Respiratory Infection

“Sometimes we need education in the obvious more than investigation of the obscure.”

–Oliver Wendell Holmes

In my meanderings across the blogosphere, opinion pages, talk radio, Facebook, and even chatting with friends and acquaintances, I continually encounter folks who assert that masking is ineffective for protection against respiratory infections. Of course they never provide evidence to support their claim beyond their confidence that they are correct. I often reply that they should invite their next surgeon to remove his mask during the operation. I have published in these pages a few articles showing how controlled trials and real-life empirical data show this to be wrong (see here, here and here).

Now a new meta-analysis by University of Oxford researchers, or an analysis of some 400 published studies on facemasks, further confirms that if they are correctly and consistently worn masks effectively protect against respiratory infections, including COVID. The study also concludes that mask mandates are effective in reducing community transmission of respiratory pathogens. Note that health mandates have long passed Constitutional muster as I reported earlier. This new analysis was triggered by the controversial 2023 Cochrane review of non-pharmaceutical interventions for COVID, which several publications reported showed that masks were ineffective. However, Cochrane’s editor-in-chief later stated publicly that the review did not support such a conclusion and issued an apology for the confusion and a clarification. Several scholars also questioned the review’s methods and found flaws in its meta-analysis and criticized it for omitting a vast body of non-trial evidence. Hence the Oxford study was undertaken to learn the truth about the efficacy of face masks.

Face masks, along with other non-pharmaceutical measures, such as social isolation, have long been used during infectious epidemics, especially when vaccines and antibiotics were not available. This goes back to the European bubonic plague in 1619, the Great Manchurian plague (1910), the 1918 Spanish flu, etc. When there is no vaccine or therapeutic intervention to treat an infectious disease, physical isolation measures, such as social distancing, quarantine, and masks are critical.

The Oxford study. The study examined the relevant literature in a wide range of disciplines (public health, epidemiology, infectious diseases, biosecurity, fluid dynamics, materials science, modeling, data science, clinical trials, sociology, anthropology, psychology, and occupational hygiene). This included numerous randomly controlled trials as well as observational, or “real-world,” evidence. The results convincingly showed that cloth face coverings and disposable medical masks that are handed out at your doctor’s office can reduce infection risk, but the N95 respirators are much better.

In the early COVID-19 pandemic, when randomly controlled trials of masks had not yet been done, the study’s authors found a systematic review and meta-analysis of observational studies reporting that respirators and masks decreased infection risk up to 85%. Further, in a school-based cohort study, the risk of COVID among the family members of students was reduced by 30% to 40% when teachers used masks.

Other case-control and cohort studies in healthcare workers provided additional evidence of substantial reductions in COVID-19 risk associated with use of respirators. In 2020, one study found over 400-times lower odds of occupational acquisition of COVID among hospital staff using N95 respirators in respiratory, intensive care, and infectious diseases departments compared to those from other departments without continuous masking.

While cloth face masks were proven to protect against airborne infection, N95 or FFP2 face-fitting respirators were most effective. The latter fit more closely to the face minimizing ambient air from leaking through the edges. They also work differently from cloth masks, which use multiple layers as a barrier to block pathogens. In contrast, respirators pass air through a specially designed filter that uses electrostatic charges to trap airborne particles, whether dust or bugs.

The pore size in typical surgical masks and respirators is larger than many viruses, like Cov-2, but, viruses do not float around the air on their own. They are carried as passengers via respiratory aerosols, which are blocked by masks. Note that the International Standards Organization (ISO) provides standards for optimum filtration for respirators. This includes lab testing for filtration efficiency. This also includes personal testing while exercising in the face of a challenge contaminant. A respirator is considered to meet requirements when it achieves a 100-fold reduction in the challenge contaminate penetrating the barrier. Respirators outperform surgical masks by 8-12-fold. These results were further confirmed with animal Cov-2 infection experiments. Infected hamsters were separated from uninfected ones by a partition make of surgical mask material, which reduced Cov-2 transmission by 75%.

Besides lab studies and randomly controlled trials of face mask use, the authors also conducted a systematic review of 44 observational studies involving SARS-1, MERS, and SARS-Cov-2. They concluded that masks and respirators reduced the risk of infection by 85%. Overall, respirators were 96% effective while surgical masks were 67% effective. This protection was “dose dependent,” meaning that protection increased with the frequency of use of masks. Masks were not only found to protect the wearer, but also were effective and preventing infection of non-mask wearers surrounding the masked person. But, the greatest protection was when both parties were masked.

In addition, the study examined the effects of mask mandates in several different settings. The first such analysis found a progressive decline in epidemic growth rates after mandates were enacted when compared to time frames immediately before the mandates. Also, masking was an effective predictor of lower infection rates in the US. An analysis of masking in Boston schools, found a surge in CoV-2 infections after February 2022, when mandates were lifted. Similar evidence demonstrating the efficacy of mask mandates was reported in many other studies. Importantly, the meta-analysis did not find any evidence for significant harm to the health of mask wearers even during strenuous exercise. Specifically, they do not increase the carbon dioxide content of inhaled air. The biggest impediment to using them was discomfort and communication difficulty for deaf people who are unable to read the lips of a mask wearer.

Study conclusions. The claim that masks do not reduce transmission of airborne pathogens is incorrect. They work. Furthermore, the level of protection increases as adherence to masking increases. Masks are a critical part of infection control during a respiratory infection epidemic.

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