Association of COVID-19 Incidence and Mortality Rates With School Reopening in Brazil During the COVID-19 Pandemic

Abstract

Importance: School closures because of COVID-19 have left 1.6 billion students around the world without in-person classes for a prolonged period. To our knowledge, no study has documented whether reopening schools in low- and middle-income countries during the pandemic was associated with increased aggregate COVID-19 incidence and mortality with appropriate counterfactuals.

Objective: To test whether reopening schools under appropriate protocols during the COVID-19 pandemic was associated with increased municipal-level COVID-19 cases and deaths in São Paulo State, Brazil.

Design setting and participants: This observational study of municipalities in São Paulo State, Brazil, uses a difference-in-differences analysis to examine the association between municipal decisions to reopen schools during the COVID-19 pandemic and municipal-level COVID-19 case and death rates between October and December 2020. The study compared 129 municipalities that reopened schools in 2020 with 514 that did not and excluded data for 2 municipalities that reopened schools and closed then again.

Main outcomes and measures: New COVID-19 cases and deaths per 10 000 inhabitants up to 12 weeks after school reopenings and municipal-level aggregate mobility for a subset of municipalities.

Results: There were 8764 schools in the 129 municipalities that reopened schools compared with 9997 in the control group of 514 municipalities that did not reopen schools. The municipalities that reopened schools had a cumulative COVID-19 incidence of 20 cases per 1000 inhabitants and mortality of 0.5 deaths per 1000 inhabitants in September 2020 (the baseline period) compared with an incidence of 18 cases per 1000 inhabitants and mortality of 0.45 deaths per 1000 inhabitants during the baseline period in the comparison group. The findings indicated that there were no statistically significant differences between municipalities that authorized schools to reopen and those that did not for (1) weekly new cases (difference-in-differences, -0.03; 95% CI, -0.09 to 0.03) and (2) weekly new deaths (difference-in-differences, -0.003; 95% CI, -0.011 to 0.004) before and after October 2020. Reopening schools was not associated with higher disease activity, even in relatively vulnerable municipalities, nor aggregate mobility.

Conclusions and relevance: The findings from this study suggest that keeping schools open during the COVID-19 pandemic did not contribute to the aggregate disease activity.

Figure 1.. Trends in the Outcomes of Interest for Municipalities That Reopened Schools and Those That Did Not

Trends for the outcomes of interest separately for municipalities that reopened schools and those that did not. Log of cases (A) and log of deaths (B) per 10 000 inhabitants. For the control group, the week of reopening was normalized to the last week of September 2020. The sample included 129 municipalities for the schools that reopened and 514 for the control group (schools that did not reopen).

Figure 2.. Trends in the Outcomes of Interest for Municipalities That Reopened Schools and Those That Did Not With a Matched Sample

Trends for the outcomes of interest separately for municipalities that reopened schools and those that did not and were the closest matches for the municipalities that reopened. Log of cases (A) and log of deaths (B). For the control group, the week of reopening was normalized to the last week of September 2020; the vertical bars represent 95% CIs. The sample included 129 municipalities for each group, those with schools that reopened and the control group (those with schools that did not).

Figure 3.. Estimates of the Difference Between the Groups Using the Difference-in-Differences Estimator

Estimated difference between municipalities that reopened schools and those that did not using the Callaway and Sant’Anna estimator. Vertical bars represent 95% CIs.

Figure 4.. Trends in Mobility Index for the Matched Sample

Trends for the Google mobility index separately for municipalities that reopened schools and those that did not and had similar characteristics as the former group. Details of the matching procedure are given in the eAppendix in the Supplement. The dependent variable represents weekly mobility compared with February 2020.