Do masks prevent COVID-19 infections? You might be thinking that it is a bit late to ponder these questions. But better late than never! As shown in the following graph provided by the CDC, COVID is here to stay with us, at least for the time being. Even though nothing compared to the 140,000 hospitalizations per week during the early 2022 wave, there were still about 40,000 weekly hospitalizations a couple of weeks back.

You might have also wondered during the various phases of the past three years which of the several masks is the most efficient to prevent COVID-19. You might also be thinking there might be hundreds of studies looking into this.

But in reality, according to a recently published systematic review, there were only three randomized controlled trials (RTC) looking at the comparative efficiency of different types of masks to reduce COVID-19 transmission published during the period between January 2020 and January 2023. Two of these studies were conducted in a community setting, and only one was conducted in a health care setting.

However, the authors included 16 observational studies (2 in community settings and 14 in health care settings) to answer this question in their analysis because of a paucity of RCTs. The studies were heterogeneous in their methodology, setting, and timing. They concluded that studies favored wearing a high-quality mask such as N95. However, the authors point out the high risk of bias in all these studies.

A November 2022 article written by Loeb et al. in Annals of Internal Medicine (which was included in the above systematic review) compared surgical masks to N95 masks among health care workers who provided routine care to suspected or confirmed COVID-19 patients. They used a pragmatic randomized trial approach comparing medical masks versus N95 masks. The study was conducted in multiple countries, such as Canada, Israel, Pakistan, and Egypt. The results were inconclusive even though N95 mask wearers experienced a slightly lower incidence of COVID-19 compared to the surgical masks (10.5 percent versus 9.3 percent).

There were several criticisms about the study. The study was done between May 2020 to March 2022. Commentators wondered about the ethics of using ordinary medical masks in such a situation while we already knew by late 2020 that COVID-19 was predominantly spread by aerosols, to which N95 masks offer superior protection. The study was also limited by the usage of masks only during direct care to the patients. Health care workers were not instructed to wear masks elsewhere, and they could easily get infected outside the care setting. The study settings were also very disparate and varied from emergency departments to long-term care facilities. There were waves of COVID-19 strains with different degrees of infectivity during the study, which also confounded the trial.

The question of the efficacy of different masks in preventing COVID-19 is complex. For example, efficacy in a highly infective situation, such as an emergency room, could be vastly different from a low-risk situation, such as a summer outdoor gathering. It also depends on several other factors, such as personal risk, the amount of time spent at the location, the infectivity of strains in circulation at a given time, and the location.

The systematic review also addressed two other issues: the use of masks and the role of mask mandates to reduce infections. Again, the authors struggled to find RCTs and included observational studies in their analysis. Regarding the first question, they were only able to find 2 RCTs and used a total of 47 observational studies. They found that masks reduced transmission in a great majority of studies, but they felt the quality of evidence was low.

They studied 18 observational studies about mask mandates and concluded that mask mandates reduced transmission but again felt that the quality of evidence was low.

Strategic masking

Recently, the concept of “strategic masking” has evolved to address these concerns. The idea is to wear a mask when it matters the most. This protocol recommends masking after assessing the personal risk and taking into consideration other factors such as the need to protect loved ones at high risk, personal risk tolerance, nature of the variants in circulation, specific location, and the total time spent at a location. Everyone can choose their own strategy based on their assessment of the risk at any given time.

The overall lack of randomized trials early in the pandemic addressing a simple basic question, such as the efficacy of masks, is interesting to note. I would not characterize this as a total failure of our research system, given that the pandemic has surprised everyone and it was highly contagious. Moreover, taking care of the patients became a priority for everyone. However, once the initial shock was over, we should have been able to design appropriate trials quite rapidly to provide definitive answers to the questions that were concerning to the public. This also points to the important fact that health care research should be aligned with answering questions that are vital to patient care.

Interestingly, one of the reasons for the delay in the studies cited by Loeb et al. was the lengthy waiting period for ethics approvals and the establishment of contracts with the study sites. These issues should have been addressed at the very beginning of the pandemic by the funding agencies and federal authorities so that more research was encouraged.

The confusion about the usefulness of different types of masks in the setting of COVID-19 probably has something to do with the ensuing controversies about COVID-19. The medical community was unable to provide definitive answers to the lingering questions from the public. There were no concrete recommendations backed by robust scientific data. This created an information vacuum and confusion in the minds of the public, which was promptly filled in by various forms of misinformation and disinformation, which continues to this day.

P. Dileep Kumar is a board-certified practicing hospitalist specializing in internal medicine. Dr. Kumar is actively engaged with professional associations such as the American College of Physicians, Michigan State Medical Society, and the American Medical Association. He has held a variety of leadership roles and has authored more than 100 publications in various medical journals and a book on rabies (Biography of Disease Series). Additionally, he has presented more than 50 papers at various national and international medical conferences. Several of his papers are widely cited in the literature and referenced in various textbooks.