Schools are an important yet politically contested space in the Covid-19 response, which makes analyses such as this one particularly relevant to decision makers. We estimated that the lifting of masking requirements in school districts in the greater Boston area during March 2022 contributed an additional 45 Covid-19 cases per 1000 students and staff during the following 15-week period. Overall, this estimate corresponded to nearly 12,000 additional Covid-19 cases among students and staff, which accounted for one third of the cases in school districts that lifted masking requirements during that time and most likely translated to substantial loss of in-person school days.
We observed that the effect of school masking policies was greatest during the weeks when the background incidences of Covid-19 in surrounding cities and towns were highest, a finding that suggests that universal masking policies may be most effective when they are implemented before and throughout periods of high SARS-CoV-2 transmission. Under the CDC guidance at that time, as well as the updated guidance issued in August 2022, universal masking would not have been recommended until the incidences of Covid-19 in schools and surrounding communities were already nearing their peak (May 2022); by this time, a substantial proportion of the effects of masking polices that we observed had already accrued. As such, relying on lagging metrics such as CDC Covid-19 Community Levels and Covid-19 hospitalizations to inform school masking policies is most likely insufficient to prevent Covid-19 cases and loss of in-person school days, and policymakers might instead consider measures of community transmission (e.g., SARS-CoV-2 wastewater concentration or Covid-19 incidence) to inform such policies.
Understanding Covid-19 policy decisions requires attention to power and existing historical and sociopolitical contexts.10,40 Structural racism and racial capitalism operate through multiple pathways, including higher levels of household crowding and employment in essential industries and lower levels of access to testing, vaccines, and treatment; these structural forces differentially concentrate the risk of both SARS-CoV-2 exposure and severe Covid-19 in low-income and Black, Latinx, and Indigenous communities.9-11,18 In our study, school districts that chose to sustain masking requirements longer tended to have school buildings in worse physical condition and more students per classroom, and these districts had higher percentages of students and staff already made vulnerable by historical and contemporary systems of oppression (e.g., racism, capitalism, xenophobia, and ableism). In Boston and Chelsea, more than 80% of the students are Black, Latinx, or people of color, and these cities were among the Massachusetts cities and towns that were hit hardest by Covid-19. Students and families in these school districts have strongly advocated and organized for governmental action to increase Covid-19 protections in schools, emphasizing their role as essential workers, the risk to vulnerable family members, and the unequal consequences of missed work and school.41,42 The decision in some school districts to sustain school masking policies longer may therefore reflect an understanding among parents and elected officials that structural racism is embedded in public policies and that policy decisions have the potential to rectify or reproduce health inequities.10,14,16,40
A growing body of work suggests that knowledge of differential conditions and inequitable effects may decrease support for Covid-19 protections among systematically advantaged groups, whose relative position largely insulates them from Covid-19 harms, while simultaneously increasing support among groups that are directly affected by systems of oppression.43-45 For example, in a randomized trial in which White persons were assigned to receive information about structural causes of persistent Covid-19 inequities across racial or ethnic groups or to not receive such information, those who received the information were less likely to support Covid-19 prevention policies and were less likely to report individual concern about Covid-19 and empathy for the groups that were most affected.45 In several studies and polls, Black and Latinx parents were more likely than White parents to support school masking requirements and less likely to have confidence that schools could operate safely without additional protections.43,44,46 Failure to consider unequal baseline conditions and ongoing inequitable effects of Covid-19 policies risks further exacerbating inequities in Covid-19 incidence and educational outcomes.
Because universal masking policies in schools have been contentious, we anticipate several critiques. One such critique is that the benefits of universal masking in schools are outstripped by potential disruptions to teaching, learning, and social development. These effects warrant further rigorous evaluation; however, to date, there is no clear existing evidence that masking inhibits learning or harms development.47,48 In addition, such effects might be considered alongside the spectrum of benefits of universal masking, including fewer missed school days and staffing shortages, reduced risk of illness for students and their families, and reduced economic hardship for caregivers, who might miss work if their child is sick or if they become ill themselves. For example, in Lexington, MA, a comparison district approximately 10 miles from Boston, mean student and staff absences due to Covid-19 during weeks when masking was optional were 50% higher than absences during previous weeks, when masking was required (see the Supplementary Appendix).
In addition, severe Covid-19 and post-Covid conditions remain substantial risks among school-age children. Like much of the United States, the greater Boston area has low Covid-19 vaccination coverage among children (only 53% of children 5 to 11 years of age had been fully vaccinated in Boston and Chelsea through October 2022, as compared with 67% in comparison districts), with substantial inequities according to race or ethnic group and socioeconomic status. Furthermore, we observed greater benefits of sustaining masking among staff, a finding that emphasizes that universal masking is an important component of comprehensive workplace protections for staff, who may be at a higher risk for severe Covid-19 than students. In addition, staff absences may be especially consequential for students who need additional educational supports and services, including ELL students and students with disabilities.
A second common critique is that there are alternative approaches to reducing transmission and severe disease, such as improved ventilation and increased vaccination coverage. Our findings show that the better ventilation and higher vaccination coverage in school districts that lifted masking requirements than in districts that sustained masking requirements were insufficient to prevent all Covid-19 cases in these schools. Therefore, although we cannot weigh the full spectrum of individual and societal implications of masking policies, our study highlights the important role of interim universal school masking policies in mitigating the effects of Covid-19 while longer-term, more sustainable policies are developed to increase vaccination uptake and improve learning environments.
A key strength of this study is our use of difference-in-differences methods with staggered dates of the lifting of masking requirements. Although there are some factors related to SARS-CoV-2 exposure that differed across school districts, difference-in-differences methods yield robust analyses in the context of sources of confounding that do not change over time (e.g., sociodemographic characteristics or building conditions) or do not coincide with the policy change of interest. In sensitivity analyses, the benefits of masking requirements persisted after we controlled for Covid-19 indicators at the community level, vaccination coverage, and previous incidence of infection. Furthermore, we found that school districts that lifted masking requirements were districts that would have been expected to have lower incidences of Covid-19 (on average, they had buildings in better physical condition and had higher vaccination coverage), which suggests that any residual confounding by Covid-19 risk would have led to underestimation of the harms of lifting masking requirements overall.
A limitation of this study is that we did not have data regarding Covid-19 testing in individual school districts. However, DESE ended the practice of required testing of only unmasked close contacts in January 2022, and data from that “test-and-stay” program show that far too few schools continued with the program for it to explain our results. Under the most extreme assumptions, additional testing of unmasked close contacts could explain less than 7% of the estimated excess cases. Overall, our findings should be interpreted as the effect of universal masking policies and not as the effect of masking per se, since masks were still encouraged in most school settings. Despite this consideration, the effect of lifting masking requirements was substantial.
The winter wave of the B.1.1.529 (omicron) variant during the 2021–2022 school year will not be the final Covid-19 surge to affect students and staff, and ongoing efforts to address inequitable environmental risks and effects of Covid-19 in school settings are urgently needed. Our results support that universal masking with high-quality masks or respirators during periods of high community transmission is an important strategy for minimizing SARS-CoV-2 spread and loss of in-person school days. Our results also suggest that universal masking may be an important tool for mitigating the effects of structural racism in schools, including the differential risk of severe Covid-19, educational disruptions, and health and economic effects of secondary transmission to household members. School districts could use these findings to develop equitable mitigation plans in anticipation of a potential winter Covid-19 wave during the 2022–2023 school year, as well as clear decision thresholds for removing masks as the wave abates.