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.

Abstract

BackgroundThe 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.MethodsWe 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.ResultsOverall, 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.ConclusionThe present study showed that the effects of COVID‐19 vaccination on menstruation seem limited.