While the COVID-19 vaccines have made a dramatic difference in controlling the pandemic, researchers are still learning about the ways that the shots may affect people’s health.
One of those questions centers around how the vaccines might impact menstrual cycles. Reports of women experiencing changes in their cycles—either in the intensity and frequency of bleeding, or the length of their periods—have prompted more rigorous investigations of how COVID-19 vaccines may be affecting cycles.
In the latest study, published in the BMJ, researchers led by Rickard Ljung, professor of epidemiology and physician specialist at the Swedish Medical Products Agency (the country’s equivalent to the U.S. Food and Drug Administration), looked at medical records from nearly 3 million Swedish women, ages 12 to 74. They focused on those who had sought care from health care professionals for menstrual changes from Dec. 2020 to Feb. 2022 and were able to see when the women were vaccinated and how long after their immunization they sought care.
That analysis found no strong association between COVID-19 vaccines and changes in menstruation—or at least bleeding events that were severe enough for women to seek medical care.