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Mask Use and Ventilation Improvements to Reduce COVID-19 Incidence in Elementary Schools – Georgia, November 16-December 11, 2020

Our take —

In this study of 169 K-5th grade schools in the U.S. state of Georgia during late 2020, schools that required masks for teachers and staff had 37% lower incidence of COVID-19 relative to those that did not. Similarly, schools that had some form of improved ventilation (e.g., opened doors or windows) had 39% lower incidence of COVID-19 relative to schools without improved ventilation. However, only a small proportion of schools in Georgia responded to the survey, and the analyses were not adjusted for many possible factors that could have confounded the results, including the presence or absence of other interventions (for example, schools that required masks may have been more likely to improve ventilation). For these reasons, the associations observed here can only be regarded as exploratory.

Study design

Ecological

Study population and setting

This study estimated associations between school-level COVID-19 prevention strategies (including improved ventilation and mask requirements) and COVID-19 incidence. The study included 169 schools (kindergarten – 5th grade) in Georgia, USA that responded to a survey on COVID-19 prevention strategies and reported COVID-19 incidence from November 16 to December 11, 2020. The Georgia Department of Education emailed a survey to all 1,321 public K-5 schools and 140 private schools to measure prevention strategies including mask requirements for staff and students, ventilation improvements (defined as dilution methods, e.g., opening windows and using fans; or filtration methods, e.g., HEPA filters), flexible medical leave for staff, spacing desks six feet or more apart, and placing barriers between all desks. COVID-19 cases were reported by schools to the Georgia Department of Public Health. The authors used negative binomial regression models to estimate risk ratios for each intervention individually, adjusted for county-level COVID-19 incidence.

Summary of Main Findings

Schools had a median of 532 students with a median class size of 19 students; the median proportion of in-person students at each school was 85%. The majority of schools required masks for staff (65%) and students (52%), offered flexible medical leave for staff (82%), and improved ventilation systems (52%). Fewer schools placed barriers between desks (22%) or spaced desks six feet or more apart (19%). COVID-19 incidence among staff and students during the study period was 3.08 per 500 enrolled students, which was lower than the 5.28 per 500 population observed in counties with participating schools during the same period. Mask requirements for staff members were associated with lower COVID-19 incidence (risk ratio (RR): 0.63, 95% CI: 0.47 to 0.85); student mask requirements had an RR of 0.79 but were not statistically significant (95% CI: 0.50 to 1.08). Improved ventilation was also associated with lower incidence (0.61, 0.43 to 0.87). Those with dilution improvements only had lower COVID-19 incidence than those without any improvements (0.65, 0.43 to 0.98), while those with filtration only did not have statistically significant lower incidence (0.69, 0.40 to 1.21) compared to those without improvements.

Study Strengths

The survey elicited some specifics on the type of ventilation improvements enacted by schools.

Limitations

The analyses considered each intervention one at a time, only adjusting for county-level COVID-19 incidence. In addition to the standard concerns over unmeasured confounding from such an analysis (e.g., by socioeconomic status, class size, etc.), interventions were likely correlated with one another. For example, if schools with staff mask requirements were also likely to have improved ventilation, then one cannot conclude from these results that either intervention has an independent effect on COVID-19 incidence. Additionally, COVID-19 incidence was derived from school self-report, and there may have been systematic under-ascertainment that varied along with interventions. Finally, the survey response rate was low (12%), and participating schools may not be representative of all Georgia K-5 schools. In particular, those schools with higher COVID-19 incidence rates or ineffective interventions may have been less likely to participate.

Value added

This is one of the first studies to estimate effects of improved ventilation on COVID-19 outcomes, particularly in educational settings.

This review was posted on: 19 June 2021