Experts study COVID-19 vaccines’ impact on menstruation Updated Apr 14, 2021; Posted Apr 14, 2021 Syringes containing vaccine stand at the ready for members of the public to get the vaccine administered to them in the Sullivan County Elementary School in Laporte Bourgh Sullivan County Pennsylvania Fred Adams/for Spotlight PA 1-29-21 Facebook Share An unexpected side effect of the COVID-19 vaccine has prompted experts to take a closer look at how menstrual cycles are impacted following the shot, reports say. Katherine Lee, a post-doctoral scholar in the public health sciences division at the University of Washington School of Medicine in St. Louis, told TODAY she and a colleague discussed their side effects after taking the vaccine. Turns out both of them had experienced an unexpected change in their menstrual cycle.