An informative resource to this effect is, actually, the Cochrane Review on the same topic published in 2011.⁹ Curiously, this version was led by much the same authorship team as the present version, but arriving at quite different conclusions. The primary difference, other than including studies only up through 2010, was the inclusion of any comparative design in which some attempt was made to control for confounding. This included case-control, before-and-after, and other quasi-experimental designs.

The results are starkly different. These additional studies include those evaluating use of simple surgical masks comprising over 3,000 participants during the initial Severe Acute Respiratory Syndrome (SARS) epidemic in 2003. In these case-control studies, those wearing a mask were one-third as likely as controls to contract SARS. Fewer case-control studies assessed the use of N95 respirators, but the risk for contracting SARS was halved yet again in those who regularly wore N95 masks when caring for infected cases. In contrast to the present-day apparent inability to draw conclusions regarding masks, the pre-pandemic view of these same authors was: “Simple and low-cost interventions would be useful for reducing transmission of epidemic respiratory viruses.”

These previously included studies also require the same critical eye as those trials included in the most recent review, and possess their own limitations and generalizability issues. However, it is fallacious and unserious to suggest a lack of relevance to the present day, or to imply the most recent Cochrane Review has any bearing on the question of whether masks “work.” Rather than addressing mask efficacy, which is still best informed by the those original studies, the more recent trials raise a different question regarding the effectiveness of mask recommendations. Masking certainly reduces viral transmission, but in order to develop relevant infection control effects at a population level, other factors relating to mask use, uptake, and other public health measures require consideration. Regrettably, in self-reinforcing fashion, casting doubt upon the efficacy of masks ultimately diminishes their population-level effectiveness, a vicious cycle favoring those who decry the usefulness of masks.

As the pandemic winds down, more individuals have durable protection against severe disease and community viral prevalence is subsiding. These factors make routine mask use dramatically less important than early in the pandemic. However, preventing mischaracterization of these data, and other specious representations of studies, remains critical preparation for future public health activities.

Dr. Radecki is an emergency physician and informatician with Christchurch Hospital in Christchurch, New Zealand. He is the Annals of Emergency Medicine podcast co-host and Journal Club editor and can be found on Twitter @emlitofnote.