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. 2022 Nov;16(6):1026-1032.
doi: 10.1111/irv.13027. Epub 2022 Jul 27.

Impact of the Coming-of-Age Day and ceremony on the risk of SARS-CoV-2 transmission in Japan: A natural-experimental study based on national surveillance data

Yura K Ko  1   2 , Ryo Kinoshita  1 , Masato Yamauchi  1 , Kanako Otani  1 , Taro Kamigaki  1 , Kazuki Kasuya  1   3 , Daisuke Yoneoka  1 , Yuzo Arima  1 , Yusuke Kobayashi  1 , Takeshi Arashiro  1 , Miyako Otsuka  1 , Reiko Shimbashi  1 , Motoi Suzuki  1
Affiliations

Impact of the Coming-of-Age Day and ceremony on the risk of SARS-CoV-2 transmission in Japan: A natural-experimental study based on national surveillance data

Yura K Ko et al. Influenza Other Respir Viruses. 2022 Nov.

Abstract

Background: Quantifying the impact on COVID-19 transmission from a single event has been difficult due to the virus transmission dynamics, such as lag from exposure to reported infection, non-linearity arising from the person-to-person transmission, and the modifying effects of non-pharmaceutical interventions over time. To address these issues, we aimed to estimate the COVID-19 transmission risk of social events focusing on the Japanese Coming-of-Age Day and Coming-of-Age ceremony in which "new adults" practice risky behavior on that particular day.

Methods: Using national surveillance data in Japan in 2021 and 2022, we conducted difference-in-differences regression against COVID-19 incidences by setting "new adults" cases as the treatment group and the cases 1 year younger or older than these "new adults" as the control group. In addition, we employed a triple differences approach to estimate the risk of holding the Coming-Age ceremony by using a binary variable regarding the presence or absence of the ceremony in each municipality.

Results: We estimated the relative risks (RRs) of the Coming-of-Age Day as 1.27 (95% confidence interval [CI] 1.02-1.57) in 2021 and 3.22 (95% CI 2.68-3.86) in 2022. The RR of the Coming-of-Age ceremony was also large, estimated as 2.83 (1.81-4.43) in 2022.

Conclusions: When planning large social events, it is important to be aware of the unique risks associated with these gatherings, along with effective public health messages to best communicate these risks.

Keywords: COVID-19; Coming-of-Age Day; SARS-CoV-2; non-pharmaceutical intervention; social gatherings.

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Conflict of interest statement

The authors declare no competing interests.

Figures

FIGURE 1
FIGURE 1
Epidemic curves for all age cohorts and 20‐year‐old age cohort in Japan in 2021 and January 2022. The red and black lines indicate the percentage of 20‐year‐old age cohort among all cases and the date of the Coming‐of‐Age Day, respectively.
FIGURE 2
FIGURE 2
Epidemic curves for cases of the 10‐, 19‐, 20‐, 21‐, 30‐, and 70‐year‐old age cohorts in 2021 and 2022. The black line indicates the date of the Coming‐of‐Age Day.
See this image and copyright information in PMC

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