Impact of lifting school mask mandates on community SARS-CoV-2 cases, hospitalizations, and deaths: a retrospective observational study

Abstract

Background: School masking mandates were widely adopted as a pandemic control measure, however, limited data are available regarding their effectiveness as a strategy for reducing burden of disease in the surrounding community.

Objective: To evaluate the impact of school masking policy de-adoption (mask-lifting) on SARS-CoV-2 incidence rates, hospitalizations, and deaths in the surrounding community.

Methods: Design: Retrospective observational study with an event study design, a difference-in-difference method; a target trial emulation (TTE) framework was applied as a secondary analysis. Cohort creation: Data collected from 9/2021 to 6/2022 on SARS-CoV-2 cases, hospitalizations, deaths and vaccination rates were combined with district-level masking policy data. Analysis: In the event study, the impact of masking policy de-adoption on SARS-CoV-2 cases per 100,000 county residents stratified by age during the 8-week period following the policy change was estimated. Effects on hospitalization and deaths per 1,000,000 residents were secondarily estimated. In a secondary analysis, a target trial emulation framework was applied to estimate average treatment effects.

Results: N = 3,970 districts composed of 53,453 schools were included in the cohort. In the event study, no consistent trends for COVID-19 case rates were identified for the whole cohort or for any age group. For the whole cohort, there was a statistically significant increase found 6-8 weeks following the policy change (maximum increase, 1.91 hospitalizations per 1,000,000 county residents); increases in hospitalizations were also found in the stratified analysis for all age groups, although absolute impacts were small. An increase in deaths was found during the period from 4 to 7 weeks following the policy change (maximum increase 0.62 deaths per 1,000,000 residents). In the stratified analysis, small increases in death rates were seen in 50-69 year olds (range, 0.088-1.49) and >70 year olds (range, 0.23-2.58) but not in younger groups. In the TTE framework, cases, hospitalizations, and deaths were similar in control and intervention counties.

Conclusion: This study evaluating the impact of lifting of mask mandates in schools, analyzed in two ways, was consistent results ranging from no impact to a small but statistically significant impact of the policy change on SARS-CoV-2 case and severe outcomes rates in the surrounding community. Findings can be used to inform future pandemic policy responses for elementary and secondary schools.

Keywords: COVID-19; SARS-CoV-2; healthcare policies; infection prevention; mask; respiratory virus; schools.

Figure 1

A timeline of key US Centers for Disease Control and Prevention policy recommendations and other critical milestones. Timeline created based on information gathered by Education Week and the Boston Herald (6, 7).

Figure 2

A theoretical model of the role schools play in SARS-CoV-2 spread in the community and the hypothetical impact of masks on reducing spread. Panel A depicts in-school contacts hypothetically leading to spread within the home which then leads to spread within the community and attributable hospitalizations among older adults at higher risk of severe COVID-19. Panel B depicts the hypothetical impact of in-school masking policies on the community. In this scenario, masking prevents transmission of SARS-CoV-2 in schools and this reduction leads to lower in-home and community transmission. When community transmission is lowered via mitigation in schools, severe outcomes among older adults are prevented.

Figure 3

Cohort flow diagram for included and excluded counties. Description of cohort inclusion and exclusion criteria.