The San Francisco Chronicle ran an op-ed by four physicians claiming that “Mask mandates are not effective” (Open Forum, April 19). They are part of a larger group that are advocating for the “Urgency of Normal.” Parents have used their views to call for ending mask mandates in schools as being ineffective.

However, these experts’ analysis ignores the strongest evidence of the effectiveness of masks. We had a “control” during the 2019-21 period — the dramatic decline in the influenza rate.

In the 2019-20 season, 22,000 died of flu based on data from the Centers for Disease Control and Prevention (CDC). In the 2020-21 season, about 750 died–a decline of 96%. In 2021-22, deaths are estimated to be up to 7,700 which is still at least 60% below pre-pandemic levels. We had many more social interactions but still had mask mandates in many settings which leads to the conclusion that masks have been a major contributor to reducing transmission of both influenza and COVID-19.

Part of the decline might be from some dying from COVID instead, but overlap in cases was far from 100%. The one constant throughout has been the prevalence of masks. Epidemiological data is much more compelling than the quasi-controlled studies that the physicians refer to, especially when we have such a clear control. The experts must fully explain the dramatic decline in flu mortality before they can dismiss the effectiveness of masks.