Breeding Grounds

Should schools close in the event of an infectious disease epidemic? This is not an easy question for governments to answer in an evidence-based way. Few studies exist on the epidemiology of SARS-Cov-2 in schools because of the challenges of differentiating school interventions from local isolation and social distancing measures. It is clear that new methods are needed to robustly quantify the association of school attendance with transmission rates of newly emerged pathogens or variants.

Addressing this gap, researchers in California, USA, used regression discontinuity methods to investigate the link between school eligibility and COVID-19 incidence among young children in the state. The findings, published in JAMA Network Open, revealed that children eligible for kindergarten had higher COVID-19 incidence rates than those slightly younger, especially during semesters of in-person instruction. The research spanned May 2020 to December 2022 and included 688,278 COVID-19 cases and 1,423 hospitalizations among children close to the eligibility age for kindergarten.

The study found that, during the fall 2021 semester, COVID-19 incidence was 51.5 percent higher among school-eligible children than their non-eligible peers. This trend persisted into subsequent semesters, with spring 2022 showing a 26.3 percent increase and fall 2022 a 19.1 percent increase. Despite higher incidence rates during the winter break following in-person semesters, the summer 2022 break showed a decline. These results suggest lingering effects from in-person exposure rather than from out-of-school contacts alone.

The researchers adjusted for higher COVID-19 testing rates among school-aged children, which could bias results. Weighted analyses showed consistency with unadjusted findings, supporting the robustness of the observed associations. The study did not find significant differences in hospitalization rates between the two groups, possibly due to the rarity of severe outcomes in children.

County-level data indicated that school eligibility’s impact on COVID-19 incidence was less pronounced in more populous areas, likely due to stricter mitigation measures, such as extended mask mandates. Out-of-school exposures, such as transportation and extracurricular activities, may contribute to transmission but could not be fully disentangled from classroom-based interactions.

Overall, the study supports targeted mitigation measures within schools to minimize transmission risks while preserving educational access. Moreover, the methodology used in the study may serve as a model for studying the interaction between school attendance and other infectious diseases in the future.

^{Image credit: Adobe Stock (edited)}