Jennifer Couzin-Frankel

Between April and October 2021, the survey welcomed anyone 18 and older who gets or used to get a period … a whopping 42% of about 16,000 people in the survey who had a regular menstrual cycle said they bled more heavily than usual after vaccination, a number far higher than others have reported. 

… Given their anthropology background, Clancy and Lee focused their survey on obtaining narrative-style responses and on documenting symptoms, such as breakthrough bleeding, that are important but can be hard to measure quantitatively. 

… The survey results, even with the authors’ caveats, could lead to concern that the chance of menstrual irregularities after vaccination is much higher than it actually is.