Lifting Universal Masking in Schools - Covid-19 Incidence among Students and Staff

Abstract

Background: In February 2022, Massachusetts rescinded a statewide universal masking policy in public schools, and many Massachusetts school districts lifted masking requirements during the subsequent weeks. In the greater Boston area, only two school districts - the Boston and neighboring Chelsea districts - sustained masking requirements through June 2022. The staggered lifting of masking requirements provided an opportunity to examine the effect of universal masking policies on the incidence of coronavirus disease 2019 (Covid-19) in schools.

Methods: We used a difference-in-differences analysis for staggered policy implementation to compare the incidence of Covid-19 among students and staff in school districts in the greater Boston area that lifted masking requirements with the incidence in districts that sustained masking requirements during the 2021-2022 school year. Characteristics of the school districts were also compared.

Results: Before the statewide masking policy was rescinded, trends in the incidence of Covid-19 were similar across school districts. During the 15 weeks after the statewide masking policy was rescinded, the lifting of masking requirements was associated with an additional 44.9 cases per 1000 students and staff (95% confidence interval, 32.6 to 57.1), which corresponded to an estimated 11,901 cases and to 29.4% of the cases in all districts during that time. Districts that chose to sustain masking requirements longer tended to have school buildings that were older and in worse condition and to have more students per classroom than districts that chose to lift masking requirements earlier. In addition, these districts had higher percentages of low-income students, students with disabilities, and students who were English-language learners, as well as higher percentages of Black and Latinx students and staff. Our results support universal masking as an important strategy for reducing Covid-19 incidence in schools and loss of in-person school days. As such, we believe that universal masking may be especially useful for mitigating effects of structural racism in schools, including potential deepening of educational inequities.

Conclusions: Among school districts in the greater Boston area, the lifting of masking requirements was associated with an additional 44.9 Covid-19 cases per 1000 students and staff during the 15 weeks after the statewide masking policy was rescinded.

Figure 1. Incidence of Covid-19 in School Districts in the Greater Boston Area before and after the Statewide Masking Policy Was Rescinded.

The observed incidence of coronavirus disease 2019 (Covid-19) (weekly Covid-19 cases per 1000 population) among students and staff overall (Panel A), among students alone (Panel B), and among staff alone (Panel C) is shown for the 72 school districts in the greater Boston area that were included in the study. The greater Boston area was defined according to the U.S. Census Bureau as the New England city and town area of Boston–Cambridge–Newton. The Massachusetts Department of Elementary and Secondary Education rescinded the statewide masking policy on February 28, 2022. The incidence is shown according to whether the school district lifted its masking requirement in the first, second, or third reporting week after the statewide masking policy was rescinded or the district sustained its masking requirement. A school district was considered to have lifted its masking requirement in a given reporting week if the requirement had been lifted before the first day of the reporting week (reporting weeks start on Thursday). The dashed lines indicate the first (1), second (2), and third (3) school weeks (school weeks start on Monday) during which school districts lifted masking requirements. A total of 46 school districts lifted masking requirements during the first school week (starting on February 28, 2022) and in the first reporting week (starting on March 3, 2022) after the statewide masking policy was rescinded; 17 districts lifted masking requirements during the second school week (starting on March 7, 2022) and in the second reporting week (starting on March 10, 2022); 7 districts lifted masking requirements during the third school week (starting on March 14, 2022) and in the third reporting week (starting on March 17, 2022); and 2 districts sustained masking requirements. Data points are shown on the first day of the reporting week and represent 3-week trailing rolling averages to reduce statistical noise. Dates on the x axis are restricted to the period immediately before and after the statewide masking policy was rescinded.

Figure 2. Difference-in-Differences Estimates of Additional Weekly and Cumulative Covid-19 Cases Associated with the Lifting of Masking Requirements.

Difference-in-differences models were used to estimate the difference in the change in the incidence of Covid-19 between school districts that lifted masking requirements and school districts that sustained masking requirements in each reporting week among students and staff overall, among students alone, and among staff alone, with estimates calculated on a weekly basis (Panel A) and on a cumulative basis (Panel B). 𝙸 bars and blue shading indicate 95% confidence intervals for weekly and cumulative differences, respectively. Estimates are shown according to reporting weeks since masking requirements were lifted. Vertical dashed lines indicate the first reporting week in which masking requirements were lifted in each school district; because the reporting week in which masking requirements were lifted varied according to district, the vertical dashed lines represent different calendar weeks for different school districts, depending on when masking requirements were lifted. Values in light blue and dark blue show differences during the reporting weeks before and after masking requirements were lifted, respectively. Horizontal dashed lines correspond to no difference; values above the line show additional Covid-19 cases. Gray shading indicates the initial period of peak infection with the BA.1 subvariant of the B.1.1.529 (omicron) variant (December 2021 through January 2022). Details regarding the difference-in-differences analysis are provided in the Supplementary Appendix.

Figure 3. Characteristics of the School Districts.

Data regarding the following school-district characteristics are shown: distribution of students in populations selected and defined by the Massachusetts Department of Elementary and Secondary Education (DESE), including low-income students, students with disabilities, and English-language learner (ELL) students (Panel A); distribution of students according to race or ethnic group (Panel B); distribution of staff according to race or ethnic group (Panel C); and scores for building conditions and learning environment (Panel D). The data are shown in scaled variable values so that all variables can be depicted on the same scale; the scaled variable value reflects the difference from the mean value in standard deviations. Dashed lines indicate the mean value across all school districts. Dots indicate values for individual school districts. In the box plots, horizontal bars indicate the median value, boxes the interquartile range, whiskers the value 1.5 times the interquartile range, and diamonds the mean value. Data are plotted according to whether the school district had chosen to lift its masking requirement in the first, second, or third reporting week after the statewide masking policy was rescinded or the district had chosen to sustain its masking requirement. The data shown in Panels A, B, and C are for the 2021–2022 school year and were obtained from DESE. The data shown in Panel D were obtained from the Massachusetts School Building Authority 2016–2017 school survey (most recent data).