When mass vaccination against COVID-19 started in 2021, some women noticed changes in their menstrual cycles after receiving the vaccines. Anecdotal evidence of significantly heavier bleeding and longer cycles—more days between each period—became common knowledge. While a certain amount of change in menstrual cycles is considered normal and the changes seemed only temporary, the occurrence was at least curious. It wasn’t something anyone had warned women might happen.
In late 2021, researchers started taking a closer look.
A study done in the United States, published at the beginning of January 2022, specifically researched cycle length and found only very slightly longer cycles in vaccinated women. “Change in menses length was not associated with vaccination,” it concluded. More studies of various possible effects of vaccination on menstrual cycles, female hormones, and the immune system are still underway, funded by the U.S. National Institutes of Health.
Now, the European agency that regulates pharmaceuticals is also looking into reports of changes in menstrual cycles associated with COVID-19 vaccines.
“In view of spontaneous reports of menstrual disorders with both vaccines and of findings from the literature, the [agency] decided to further assess occurrences of heavy periods or amenorrhea following vaccination,” the European Medicines Agency stated in a press release from February 11th.
It stated that it is assessing reported cases of heavy periods and absence of menstruation (amenorrhea) with the COVID-19 vaccines Comirnaty and Spikevax.
The agency also said that it had previously analysed reports of menstrual disorders in the context of reviewing data from clinical trials during the approval process for the COVID-19 vaccine and did not find that the evidence supported a causal link between the vaccines and menstrual disorders.
The press release advised that cases of menstrual disorders have also been reported following COVID-19 infection, and that changes in menstruation are very common and can occur with a wide range of underlying medical conditions as well as from stress and tiredness.
The agency said it will be doing in-depth evaluation of all available data, including reports from spontaneous reporting systems, clinical trials, and the published literature.