Sex differences in adverse event reporting rates following COVID-19 vaccination in South Korea during the pandemic

Abstract

Objectives Sex differences in adverse event (AE) reporting rates following COVID-19 vaccination were analyzed using data from South Korea’s national pharmacovigilance system. Methods We analyzed AE reports related to COVID-19 vaccines, as recorded in the Korea Adverse Event Reporting System between February 26, 2021, and December 31, 2022. AEs were classified according to the System Organ Class (SOC) and the Preferred Term (PT), as defined by the Medical Dictionary for Regulatory Activities. Reporting rates were calculated as the number of reported COVID-19 vaccine-AE pairs per 100,000 vaccine doses administered. The female-to-male (F/M) ratios were calculated by dividing the reporting rate for females by that for males, and the corresponding 95% confidence intervals (CIs) were computed. Results Among the 887,153 reported COVID-19 vaccine-AE pairs, females showed significantly higher reporting rates in 17 of the 24 SOCs, with the greatest disparity observed in infections and infestations (F/M ratio 3.21 [95% CI 3.05-3.38]). Males exhibited higher rates only for cardiac disorders (0.93 [0.89-0.98]). Among the 340 PTs, 104 exhibited significant sex differences. Females had higher reporting rates in 98 PTs, with injection site pruritus (9.00 [5.34-15.17]) showing the largest difference. Conversely, males had higher rates in six PTs, most notably for myocardial infarction (0.33 [0.18-0.60]) and cardiac arrest (0.33 [0.14-0.78]). Conclusion These findings underscore the importance of accounting for sex differences in vaccine development, clinical trials, and postmarketing safety monitoring. © 2025 The Authors.