The impact of school closures on adolescent health-related outcomes during the COVID-19 pandemic: A natural experiment in South Korea

A large number of countries implemented school closure as a response to the COVID-19 pandemic in 2020. As existing studies mostly rely on retrospective or pre/post comparisons that are prone to unmeasured confounding, the effect of school closure on adolescent health is poorly understood. The South Korean government implemented school closure to prevent the spread of COVID-19. A difference-in-differences comparing changes in health-related outcomes between provinces with differing degrees of school closure was performed. The main analysis group consists of middle school students of age 14 to 16 who were hit hardest where up to 73% of total schooling was taken online in Seoul (the physical attendance was reduced from 170 days to 45 days). For sensitivity analysis, a placebo group of high school students of age 19 who attended all school-days physically was included to detect any violation of our identification strategy. In the main analysis group of boys that experienced reduced physical school-days, both total and vigorous physical activity were reduced (-0.35 [-0.54 -0.17] days/week for vigorous physical activity and -0.38 [-0.61 -0.16] days/week for total physical activity) while such effect was absent in the placebo group of boys that actually did not experience school closure (-0.08 [-0.49 0.32] days/week for vigorous PA and -0.16 [-0.67 0.34] days/week for total PA). In girls, vigorous physical activity decreased (-0.22 [-0.40 -0.04] days/week) but the total physical activity was nearly constant (0.03 [-0.18 0.25] days/week). Other outcomes were largely unchanged.