Investigating the relationship of schools reopening to increases in COVID-19 infections using event study methodology: The case of the Delta variant

Background Hypothesis: School reopening had a significant impact on COVID-19 infection rates across USA states. Methods Eight states with fully reopened public schools were studied. States who did not previously have stay-at-home orders for a minimum of 30 days were excluded from the study so that increases in infection rates would be solely due to the economies of reopening. This study used event study methodology with a 30-day estimation window. This allowed us to determine if increases in COVID-19 infection rates were significant following schools reopening. Results Eight states were analyzed, and seven of the states had positive and significant COVID-19 infection increases. The other state’s increase was negative and significant. Conclusions This study found that reopening of schools had an initial 5-day increase in COVID-19 infections in seven of eight states whose data were examined. With schools being re-opened nationwide in Fall 2021, this indicates that with the Delta variant there is an expected significant increase in infections.