Association Between Covid-19 Vaccination and Alterations in the Menstrual Cycle

The COVID-19 pandemic, declared in March 2020 by the WHO, prompted global health strategies, including mass vaccination campaigns. In record time, vaccines were developed with various biotechnological platforms (mRNA, viral vectors and inactivated viruses), which demonstrated high efficacy in reducing hospitalizations and deaths from SARS-CoV-2. Its adverse effects were mostly mild and transient. However, as immunization progressed, anecdotal reports emerged about possible alterations in the menstrual cycle, such as changes in the duration, intensity of bleeding, frequency between cycles and atypical premenstrual symptoms. Although in cases such as the HPV vaccine this possibility had already been raised, a direct causal relationship has not been established. Objective: To analyze the possible association between vaccination against COVID-19 and menstrual alterations in Mexican university women. Materials and methods: Observational, longitudinal and analytical study by means of a digital survey applied between August and December 2024 to women over 18 years of age, active or graduated from the FES Iztacala, with regular cycles and at least one dose of COVID-19 vaccine. Those who had factors that altered their menstruation were excluded. The survey collected general data, pre- and post-vaccination menstrual characteristics, lifestyle, and vaccine type. Results: 59.8% of the participants reported menstrual alterations. The main changes were in bleeding intensity (82.6%), period length (55.4%), and frequency (31.5%). Physical and emotional symptoms were also reported. Conclusions: The results suggest a possible temporal association without serious clinical consequences.