SARS-CoV-2 Vaccination and Disorders of Menstruation: A Population-Based Cohort Study

This population-based study evaluated the association between SARS-CoV-2 vaccination and disorders of menstruation among all women in Ontario aged 18-44 years. Study exposure was receipt of a first dose of any SARS-CoV-2 vaccine from December 2021 to December 2022, handled in a time-varying manner. The outcome was an incident diagnosis of a disorder of menstruation, defined as 2 medical encounters billed as International Classification of Diseases, Ninth Revision diagnosis code 626 up to December 2023. Included were 2 114 589 women, of whom 44.7% were vaccinated against SARS-CoV-2. Disorders of menstruation occurred at a rate of 15.9 per 1000 person-years among vaccinated women, in contrast to a rate of 26.4 per 1000 person-years among unvaccinated women (adjusted rate ratio 0.60; 95% CI 0.59-0.60), supporting a lack of association between SARS-CoV-2 vaccination and an increased risk of disorders of menstruation.