Objectives: To investigate the effect of scheduled school break on circulation of influenza in young children, school-aged population and adults.

Methods: In a spatial-temporal analysis using influenza activity, school break dates, and meteorological covariates across mainland China during 2015-2018, we estimated age-specific, province-specific and overall relative risk (RR) and effectiveness of school break on influenza.

Results: We included data in 24, 25 and 17 provinces for individuals aged 0-4y, 5-19y and 20y+. We estimated a relative risk (RR) meta-estimate of 0.34 (95% CI 0.29-0.40) and an effectiveness of 66% for school break among the 5-19y. School break showed a lagged and smaller mitigation effect among the 0-4y (RR meta-estimate: 0.73, 0.68-0.79) and 20y+ (RR meta-estimate: 0.89, 0.78-1.01) versus the 5-19y.

Conclusions: The results show heterogeneous effects of school break between population subgroups, a pattern likely to hold for other respiratory infectious diseases. Our study highlights the importance of anticipating age-specific effects of implementing school closure interventions, and provides evidence for rational use of school closure interventions in future epidemics.