The association of three doses of the BNT162b2 mRNA vaccine with abnormal bleeding and an irregular menstrual cycle among premenopausal females: A single institute observation study

Background: The COVID-19 vaccine is effective in preventing severe cases of COVID-19. For women, gynecological adverse events, such as menstrual irregularities and irregular bleeding, could be a concern after COVID-19 vaccination. In this study, we investigated gynecological adverse events in the vaccinated Japanese female population. Methods: We conducted a survey-based study with health-care workers, including medical doctors and nurses, medical coworkers, and medical university faculty, staff, and students, at a single medical school and affiliated hospital in Japan. We used McNemar's test and network analysis. Results: Overall, we obtained 819 responses, and 424 were from females. After the exclusion of contradictory answers, 309 surveys were finally considered appropriate for the analysis. The frequencies of abnormal bleeding were 0.6%, 1.0%, and 3.0% for the first, second, and third doses, respectively. An irregular menstrual cycle was more common than abnormal bleeding: 1.9%, 4.9%, and 6.6% for the first, second, and third doses, respectively. Network analysis revealed that abnormal bleeding and an irregular menstrual cycle were not associated with other adverse reactions. Conclusion: The present study showed that the effects of COVID-19 vaccination on menstruation seem limited.