COVID-19 Vaccine and the Menstrual Cycle

ABSTRACT

Post-COVID-19 vaccination changes to the menstrual cycle have been reported, particularly through social media, but little evidence exists.1,2 Fewer than 200 individuals have self-reported menstrual disturbances through the Vaccine Adverse Event Reporting System. The authors of this retrospective analysis used prospectively collected menstrual cycle data from the FDA-cleared digital fertility awareness application “Natural Cycles” to assess associations between changes in the menstrual cycle or menses length and the COVID-19 vaccine. When stressors occur during the first half of the menstrual cycle (the follicular phase, when a dominant follicle is recruited and matures), cycle length can change.3 The immune response generated by mRNA vaccines could function as a stressor and temporarily affect the H-P-O axis, depending on the timing of vaccination. Because of the 21-day dosing schedule for the Pfizer mRNA vaccine and 28-day dosing schedule for the Moderna mRNA vaccine, receiving two doses in a single cycle necessitates that the first dose occurs during the early follicular phase for a normal cycling individual.