In a recent study posted to the medRxiv* preprint server, researchers evaluated the impact of removing mask mandates in schools on the incidence of coronavirus disease 2019 (COVID-19) cases.
Background
Mounting evidence suggests that universal masking effectively minimizes severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission in school and community settings. Following the updated guidelines from the Centers for Disease Control and Prevention (CDC) in February 2022, many state-wide restrictions mandating masks in schools and community settings were lifted.
While the Massachusetts (MA) Department of Elementary and Secondary Education (DESE) removed state-wide masking requirements in schools on February 28, 2022, only two school districts, Boston and Chelsea, sustained masking requirements until June 2022. This represents a unique opportunity to assess the impact of masking in schools.
About the study
In the present study, researchers examined the impact of the staggered lifting of masking requirements in schools on COVID-19 incidence in students and staff in MA school districts. They used district-level data from DESE on COVID-19 cases, enrolment, and staffing for the 2021-22 school year. Additional data on COVID-19 indicators from the surrounding communities were obtained from the MA Department of Public Health (DPH).
School districts reported COVID-19 case data every Thursday for the past seven days (Thursday to Wednesday). The study’s primary outcome was weekly COVID-19 rates among students and staff. Seventy-two school districts with 294,084 students and 46,530 staff were included in the study. The authors implemented a difference-in-differences approach with staggered implementation and compared the weekly incidence of COVID-19 between school districts with and without mask requirements.
Findings
Of the 72 school districts, 70 lifted masking requirements after the state-wide mandate was lifted, and only Boston and Chelsea public schools continued masking requirements throughout the period. Before mask mandates were removed, the COVID-19 case rates in Boston/Chelsea were similar to other regional districts, which later discontinued mask mandates. After removing the mask mandates, case rates diverged substantially between schools that sustained masking and those that removed the masking.
The difference-in-differences analysis showed no meaningful differences in the case rates before the removal of state-wide masking. Contrastingly, once mask mandates were removed, COVID-19 case rates were consistently higher in districts that removed masking requirements than those that did not. Lifting mask mandates was associated with substantial increases in the case rates among staff and students in 12 of the 15 weeks.
COVID-19 cases increased with the time since a district removed masking requirements. In the first week post-removal of masking, the authors estimated 1.44 excess cases per 1000 students and staff relative to those that sustained masking. Notably, the strength of association between COVID-19 case rates and masking requirements varied with the background COVID-19 case rates in the surrounding community.
The strongest association was noted in the weeks when community case rates were the highest for a given district. After 15 weeks (post-removal), removing mask requirements was associated with 44.9 additional COVID-19 cases per 1000 students and staff. The excess rate corresponded to 11,901 cases (> 9000 in students and nearly 3000 in staff). Intriguingly, this effect was more prominent among staff, with 81.7 excess cases per 1000 staff in schools without masking requirements.
The team noted that schools that maintained masking requirements had a higher proportion of low-income students, English-learning students, students with disabilities, and Black and Latinx students and staff. These schools had older buildings with poor physical conditions and crowded classrooms. In contrast, schools that removed masking were newer in a better condition, with fewer low-income, English-learning students and Black/Latinx students/staff.
Conclusions
The study found a significantly higher incidence of COVID-19 in schools that lifted mask requirements in February/March 2022. Specifically, removing mandates might have contributed 45 excess cases per 1000 students and staff. The MA DESE requires positive cases to isolate for five days at least or until symptoms subside. This translates to a minimum of over 17,000 days of school absence for students or > 6500 days of teacher absence in the best-case scenario.
In summary, the results underscored the importance of masking policies in schools to reduce the risk of COVID-19 among those made vulnerable by racism and other forms of oppression. The authors suggested that school districts should proactively develop mitigation policies in anticipation of a surge in the Winter during the 2022-23 school year. Specifically, enforcing mask requirements in December/January and lifting them in March or later could effectively curb the impact of COVID-19 in schools.
*Important notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.