Removing universal masking in schools is associated with increased incidence of COVID-19

1. An increased incidence of coronavirus disease 2019 (COVID-19) was seen among students and staff of school districts in Massachusetts that rescinded masking requirements.

2. The increase in incidence of COVID-19 was significantly higher among school staff than students.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Universal masking has been a critical intervention in reducing the transmission of SARS-CoV-2 within schools. A mandatory masking policy was instigated for the 2021-2022 school year in the Massachusetts Department of Elementary and Secondary Education. Masking requirements were eventually lifted by some schools beginning in February 2022. Before masking requirements were lifted, the incidence of COVID-19 in Boston and Chelsea districts was similar for all schools. The association between lifting masking mandates and an increase in COVID-19 cases was significant during 12 of the 15 weeks after policy changes. The effect of lifting masking mandates was slightly more significant among staff than students. After masking requirements were lifted, a greater incidence of COVID-19 was observed for both students and staff. Due to isolation policies after a positive test for COVID-19, the additional cases resulted in a significant increase in missed days by students and staff. The effects of lifting masking policies were greatest when the overall incidence in the surrounding city or towns was highest. School districts that chose to sustain masking requirements had a higher percentage of low-income students, students with disabilities, and Black and Latinx students and staff. A strength of this study is the various school districts examined in the data pool, which reflects the heterogeneity of the general population. Additionally, sensitivity analyses were conducted to control for factors such as socioeconomic status. A limitation of the study was that staff and students may have continued to mask regardless of the policy changes, which may impact data on COVID-19 transmission.

Click to read the study in NEJM

Relevant Reading: Evaluation of the BNT162b2 Covid-19 vaccine in children 5 to 11 years of age

In-Depth [retrospective cohort]: This study examined the weekly incidence of COVID-19 among staff and students in school districts where masking requirements were lifted. The final sample included 62 school districts totaling 46,530 staff and 294,084 students. The observed weekly incidence of COVID-19 was reported per 1,000 population. Difference-in-differences methods were used to estimate the causal effect of policy changes. Trends were followed for a total of 15 weeks after the statewide masking policy was rescinded. In the first week that masking policies were rescinded statewide, 46 school districts lifted their masking requirements. A further 17 removed them in the second week and seven in the third week. The lifting of masking requirements was associated with an additional 44.9 cases per 1,000 students and staff during the 15 weeks after policies were rescinded statewide (95% Confidence Interval [CI], 32.6 to 57.1). This is estimated to have been associated with an additional 11,901 COVID-19 cases (95% CI, 8651 to 15,151). The additional cases accounted for 33.4% of cases in school districts that lifted masking requirements (95% CI, 24.3 to 42.5) and 29.4% of the cases in all school districts (95% CI, 21.4 to 37.5). The lifting of mask mandates was associated with an additional 81.7 cases per 100 staff (95% CI, 59.3 to 104.1). The additional COVID-19 cases were associated with an estimated amount of 17,500 missed school days for students and 6,500 missed days for staff during the 15-week period. Schools that chose to sustain masking requirements longer had more low-income students, students with disabilities, and English-language learner students. Overall, the present study suggests that lifting mask mandates is associated with an increased incidence of COVID-19 at schools.

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