One can hardly blame people for being worried about the new Covid-19 vaccines when there are so many anecdotal reports of weird side effects — including women experiencing disturbing changes in their menstrual cycles. 

Reports of early and unusually heavy periods or other irregularities were becoming so common earlier this spring that University of Illinois anthropologist Kate Clancy started collecting them. People may wonder, rightly, why this isn’t being studied in a more systematic way. If something this unexpected can happen, then what else?

The original clinical trials were set up to get the minimum information needed to win emergency use approval, and follow-up study has been less than systematic. Yet getting a handle on these disturbing side effects wouldn’t be that hard. Several doctors I talked to mentioned there’s a self-reporting system called V-Safe, but they’d like to see something bigger and more systematic, where people tracked all sorts of physical changes in real time, including these peculiar menstrual irregularities.