Persistent All-Cause Excess Mortality Observed in Japan After the COVID-19 Pandemic

Introduction: Following the end of the COVID-19 pandemic, excess mortality rates declined in many countries. However, Japan’s excess mortality rate remained elevated even in 2024. Most countries have stopped administering booster vaccines on a large scale; however, Japan continues to recommend COVID-19 vaccination for elderly individuals, and its booster vaccination per capita rate is the highest in the world. This study attempted to identify the variables related to excess mortality rates during and after the pandemic.Methods: The age-adjusted numbers of deaths and excess mortality rates were calculated for Japan's 47 prefectures from 2020 to 2024. Scatter plots were generated to visualize the relationship between the excess mortality rates and doses of COVID-19 booster vaccine administered. The regression model was subsequently conducted to examine variables associated with excess mortality rates during and after the pandemic across Japan's 47 prefectures.Results: In Japan, age-adjusted excess mortality was not observed in 2020 and 2021; however, it increased to 5.9% in 2022 and 4.9% in 2023. This increase continued even in 2024, when the pandemic ended, reaching 5.7%. During the pandemic period from January to September 2022, when vaccine doses were limited to four, the age-adjusted excess mortality rate showed a negative correlation with the number of vaccine doses (r=-0.36, p=0.013). From June 2023 to September 2024, however, after the pandemic ended and doses 5 to 7 were added, a positive correlation emerged (r=0.55, p=0.000064). A multiple regression analysis showed that excess mortality rates after the pandemic was more strongly associated with the number of booster vaccine doses than with the number of COVID-19 infections and population density of the 47 prefectures. Conclusions: The findings of the present study strongly call attention to the negative aspects of frequent COVID-19 vaccination.