In February, Kate Clancy, PhD, asked her Twitter followers whether any menstruators had noticed anything odd after receiving the vaccine. “A colleague told me she has heard from others that their periods were heavy post-vax,” she wrote. “I’m a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I’m in my 20s again.” Dr Clancy’s replies were inundated with similar stories. Some said they started spotting unexpectedly; several mentioned that they were experiencing period symptoms, including cramping and bleeding, for the first time since getting IUDs or going through menopause. And similar conversations are happening elsewhere on the internet, too: There are numerous threads on Reddit tracking the relationship between menstruation and the vaccines.