One of the first studies to track whether COVID-19 vaccination might affect women’s periods found a small and temporary change.
Research published Wednesday tracked nearly 4,000 U.S. women through six menstrual cycles and on average, the next period after a shot started about a day later than usual. But there was no change in the number of days of menstrual bleeding after COVID-19 vaccination.
“This is incredibly reassuring,” said Dr. Alison Edelman of Oregon Health & Science University, who led the research and said it’s important to tell women what to expect.
Some women have reported irregular periods or other menstrual changes after their shots. The National Institutes of Health is funding studies to examine if there’s any link.
Edelman’s team analyzed data from a birth control app called Natural Cycles, cleared by the Food and Drug Administration for women to track their menstrual cycles and tell when they’re most likely to become pregnant.