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Jiaying Qiao 1 Article
Public holidays increased the transmission of COVID-19 in Japan, 2020-2021: a mathematical modelling study
Jiaying Qiao, Hiroshi Nishiura
Epidemiol Health. 2024;46:e2024025.   Published online January 22, 2024
DOI: https://doi.org/10.4178/epih.e2024025
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AbstractAbstract AbstractSummary PDFSupplementary Material
Abstract
OBJECTIVES
Although the role of specific holidays in modifying transmission dynamics of infectious diseases has received some research attention, the epidemiological impact of public holidays on the transmission of coronavirus disease 2019 (COVID-19) remains unclear.
METHODS
To assess the extent of increased transmission frequency during public holidays, we collected COVID-19 incidence and mobility data in Hokkaido, Tokyo, Aichi, and Osaka from February 15, 2020 to September 30, 2021. Models linking the estimated effective reproduction number (Rt) with raw or adjusted mobility, public holidays, and the state of emergency declaration were developed. The best-fit model included public holidays as an essential input variable, and was used to calculate counterfactuals of Rt in the absence of holidays.
RESULTS
During public holidays, on average, Rt increased by 5.71%, 3.19%, 4.84%, and 24.82% in Hokkaido, Tokyo, Aichi, and Osaka, respectively, resulting in a total increase of 580 (95% confidence interval [CI], 213 to 954), 2,209 (95% CI, 1,230 to 3,201), 1,086 (95% CI, 478 to 1,686), and 5,211 (95% CI, 4,554 to 5,867) cases that were attributable to the impact of public holidays.
CONCLUSIONS
Public holidays intensified the transmission of COVID-19, highlighting the importance of considering public holidays in designing appropriate public health and social measures in the future.
Summary
Key Message
• The number of COVID-19 cases increased during public holidays in Japan. • The increase may have occurred because of elevated mobility rate and altered contact behaviours. • The effect of holidays varied by prefecture in Japan.

Epidemiol Health : Epidemiology and Health