Analysis of the Association Between BNT162b2 mRNA COVID-19 Vaccination and Deaths Within 10 Days After Vaccination Using the Sex Ratio in Japan

Introduction: The association between coronavirus disease 2019 (COVID-19) vaccinations and deaths after vaccination has been investigated primarily through cohort and self-controlled case series studies. In the present study, the sex ratios of reported deaths were compared by period. Methods: Descriptive analysis was conducted using data on deaths reported after vaccination with the BNT162b2 mRNA vaccine. The data used were published by the Ministry of Health, Labour and Welfare in Japan. The risk period was defined as within 10 days of vaccination, and the control period was defined as 11 to 180 days after vaccination. Sex ratios were calculated for all-cause deaths and each outcome by dividing the number of males by that of females and multiplying by 100. Fisher's exact test was performed to analyze the results. Graphs were created to show the number of days from vaccination to death and that of reported deaths. Results: For all-cause deaths among individuals aged >65 years, the sex ratio during the risk period was 92, significantly lower than that during the control period (130) (p=0.0050). Conversely, for all-cause deaths among those aged <= 64 years, the sex ratio during the risk period was 204, significantly higher than that during the control period (111) (p=0.044). Reported deaths were concentrated during the risk period in both groups. Sex ratios by period for each outcome were also examined. However, the differences were not significant across any of the outcomes. Conclusion: The results indicate that the BNT162b2 mRNA vaccination may influence the occurrence of death during the risk period. In a cohort study in Japan, there was no significant increase in all-cause mortality owing to vaccination. This does not contradict the results of the present study. The results of a cohort study provide support for vaccine safety. However, this does not indicate that vaccine-related deaths are nonexistent; it only indicates that their number is not large enough to make a significant difference. Japan has relief services for adverse health effects that provide financial support to patients. On this occasion, it is difficult to determine whether a postvaccination death is incidental or vaccine-related. A self-controlled risk interval design and a comparison of sex ratios by period may be useful in examining the association between vaccination and deaths after vaccination when a cohort study does not detect a significant difference due to a low mortality rate. The latter approach may be particularly useful for analyzing data with reporting bias. The author believes that this approach may not provide conclusive evidence, but it can offer valuable insights into assessing vaccine safety.