Effect of COVID-19 vaccination on menstrual periods in a prospectively recruited cohort

COVID-19 vaccination protects against the potentially serious consequences of SARS-CoV2 infection, but some people have been hesitant to receive the vaccine because of reports that it could affect menstrual bleeding. To determine whether this occurs, we prospectively recruited a cohort of 79 individuals, each of whom recorded details of at least three consecutive menstrual cycles, during which time they each received at least one dose of COVID-19 vaccine. We find that either dose of the COVID-19 vaccine is associated with a delay to the subsequent period in spontaneously cycling participants (2.3 days after dose 1; 1.3 days after dose 2) but this change rapidly reverses. No change to timing was detected in those on hormonal contraception. We detected no change in menstrual flow associated with either dose of the vaccine, in either spontaneously cycling participants or those on hormonal contraception. We detected no association between menstrual changes and other commonly-reported side effects of vaccination, such as sore arm, fever and fatigue.