As the COVID-19 vaccines first started rolling out in the United States, an unanticipated, anecdotal side effect started to emerge: Many people speculated that the vaccine had an effect on their menstrual cycles. Studies that examined whether those anecdotes could be explained by science were sparse and small. But then, in July, the largest study of its kind added some support to the people’s claims. Tap the link in our bio to find out what researchers discovered.