Lifting Universal School Masking - Covid-19 Incidence among Students and Staff. Reply.

To the Editor: The finding by Cowger et al. (Nov. 24 issue)(1) that the lifting of universal masking in Massachusetts schools was associated with an increase in Covid-19 cases among students and staff contrasts with the findings of other robust studies.(2,3) The disparate results might be explained, in part, by uncontrolled confounding. For example, how much of the apparent effect could be explained by differing BA.1 infection-derived immunity from previous BA.1 exposure? BA.1 infection is reported to be up to 94% effective against reinfection with BA.2.(4) The community daily case incidence differed among the three main study counties during the . . .