Abandoning masking in schools during the omicron wave increased COVID-19 incidence

Référence

Cowger TL, Murray EJ, Clarke J, et al. Lifting universal masking in schools — Covid-19 incidence among students and staff. N Engl J Med 2022;387(21):1935-1946.

Sommaire

Few issues have been more contentious than universal mask requirements for children and staff in schools. There are valid concerns about balancing potential benefits (fewer cases, absences, and hospitalizations) with the potential social and educational harms. In Massachusetts, a statewide universal masking policy was in place through February 2022 at which time districts could opt to stop masking. As a result, districts in the greater Boston area rescinded universal masking requirements at different times and some districts (Boston city and Chelsea) maintained universal masking. The researchers used data from standardized weekly reporting of COVID-19 cases among students and staff to examine the effect of lifting the universal masking mandates. They used a difference-in-differences analysis that compares changes in the outcome (COVID-19 infection) between intervention and control groups. Even if there are differences between groups by population, class size, or infrastructure, the assumption is that those differences are fixed and any change in the trend is due to the intervention (lifting the mask mandate). They found that the difference in weekly COVID-19 incidence between schools that did or did not rescind masking mandates peaked at 10 cases per 1000 per week in mid-May 2022. Districts that lifted mask requirements saw 45 more COVID-19 cases per 1000 students and staff (95% CI 33 - 57), corresponding to an estimated 11,901 additional cases — despite the fact that the districts that chose to maintain masking had higher percentages of low-income students and students with disabilities, larger class sizes, and older buildings. This increase in number of additional cases was worse among staff members, who were older are more vulnerable, with 82 more cases per 1000 staff during the study period.