Whether masking requirements effectively prevented COVID-19 in schools and should be used as a mitigation strategy for future outbreaks is a highly contested issue, with children as young as two years old expected to mask up during the worst restrictions.
A reanalysis of a highly influential Boston mask study claiming continued mask mandates reduced COVID-19 cases in schools found districts that dropped masking requirements actually experienced the largest decreases in COVID-19 cases—and failed to identify any causal relationship between mask mandates and infection rates.
In a recently published preprint in arXiv, researchers reanalyzed data published in the New England Journal of Medicine (NEJM) from the Massachusetts Department of Elementary and Secondary Education and the Centers for Disease Control and Prevention to compare COVID-19 incidence in school districts that did and did not lift mask mandates.
The original NEJM study claimed lifting the statewide masking policy among school districts in the greater Boston area resulted in an additional 44.9 COVID-19 cases per 1,000 students and staff during the 15 weeks after the policy was rescinded, corresponding to an estimated 12,000 additional COVID-19 cases and to 29 percent of all cases in the school district.
Although an observational study should not be used to identify causal effects with confidence, the authors nevertheless concluded that masking requirements prevented COVID-19 cases, then used the results to justify policy decisions.
“Our results support universal masking as an important strategy for reducing Covid-19 incidence in schools and loss of in-person school days,” wrote the authors, who included researchers from Harvard University and the Boston Public Health Commission.
Furthermore, the authors encouraged school districts to use the study’s 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.”
After reanalyzing the same data using multiple methodologies, including utilizing a larger statewide control group, researchers came to a strikingly different conclusion: Schools that dropped masking requirements experienced a 22 percent decrease in COVID-19 cases compared to a 12 percent decrease in masked districts.
