International sharing of coronavirus disease 2019 (COVID-19) vaccine safety information is important for discussing the benefit-risk balance of COVID-19 vaccination at individual and population levels. We previously introduced the Japanese systems for COVID-19 vaccines safety monitoring, which represented the first and second COVID-19 vaccinations in Japan.1 The implementation of the booster (third) shot began December 2021, and the mass vaccination of children aged 5–11 years started in February 2022.