To the Editor—The 2 mRNA vaccines now administered in the United States offer >90% protection against symptomatic coronavirus disease 2019 (COVID-19) infection based on published data. How long the protection lasts beyond a few months is uncertain at the present time. There is one report of COVID-19 reinfection in an otherwise healthy adult 6 months after the initial infection despite production of neutralizing antibodies after the first infection.^{Reference Selhorst, Van Ierssel and Michiels1} This individual apparently spread COVID-19 while reinfected, likely reflecting viral replication in the nares in the absence of neutralizing antibodies at that site (ie, lack of mucosal immunity). Widespread vaccination will inevitably reduce the COVID-19 reproductive number, thereby changing the transmission dynamics in many parts of the world. However, infection among those unvaccinated and reinfection in unvaccinated and vaccinated individuals remains an ongoing concern.

Universal masking, along with other public health measures, slows COVID-19 transmission.^{Reference Leung, Chu and Shiu2,Reference Kwon, Joshi and Lo3} These interventions have also reduced transmission of other respiratory viruses over the last year,^{Reference Baker, Park, Yang, Vecchi, Metcalf and Grenfell4} thereby reducing associated morbidity and mortality.^{Reference Chow and Mermel5} The durability of protection against COVID-19 infection after vaccination is unclear, and universal masking is associated with reduced risk of COVID-19 and infection from other respiratory viruses. What will be the role of masking in the future?

Universal masking should continue until COVID-19 herd immunity is reached from natural disease and vaccination. Thereafter, particularly during winter months,^{Reference Choe, Smit and Mermel6,Reference Park, Lee, Michelow and Choe7} universal masking should continue in congregate settings and other indoor settings where social distancing cannot be maintained and/or the introduction of fresh air introduced into the environment, or filtration of recirculated air, is suboptimal.^{Reference Somsen, van Rijn, Kooij, Bem and Bonn8} Mask wearing will be particularly important for those individuals at greatest risk of poor outcomes with COVID-19 infection.⁹ By reducing transmission of respiratory viruses, masking should reduce immune selection pressure in infected individuals, and lower the likelihood that severe acute respiratory coronavirus virus 2 (SARS-CoV-2) will become more transmissible in the future.^{Reference Kemp, Datir and Collier10} There will be temptation to lower our guard and not follow advice about social distancing and masking after vaccination. However, we must learn from our experience over the past year. Failure to maintain more than a modicum of masking would reflect an inability to learn from the past to improve our lives in the future.