About half of the participants in the Covid vaccine trials were women. None of these women were asked about any changes to their menstrual cycles after receiving the vaccine and reporting their experience to researchers. The important data wasn’t collected so researchers didn’t even start investigating until many women began reporting all sorts of changes to their usual periods on social media. Women reported longer periods, heavier bleeding, or their expected periods came earlier than usual, sometimes weeks early.
Several studies have now revealed concrete evidence that Covid vaccines can indeed induce short-term changes to menstrual cycles.
“Because we had no data and people weren’t paying attention to it, individuals who started reporting it just got blown off. People feel like they were gaslighted around coming in and having these concerns,” said Alison Edelman, a professor of obstetrics and gynecology at Oregon Health and Science University.
Evidence now suggests that Covid vaccines can temporarily prolong menstruation or result in heavier periods, but that these changes tend to be short-lived, returning to normal within one or two cycles after receiving the vaccine.
One study identified a significant increase in heavier-than-normal bleeding among women ages 18-30 after getting their Covid vaccines. The study found “a significant increase in menstrual disturbances after vaccination, particularly for heavier bleeding than usual, longer duration and for short interval between menstruations.”
In another study 42% of those with regular menstrual cycles said they bled more heavily than usual after vaccination. If that isn’t alarming enough, the same study found many cases of breakthrough bleeding, people all of a sudden experiencing menstruation that no longer expect to menstruate at all. “Among respondents who typically do not menstruate, 71% of people on long-acting reversible contraceptives, 39% of people on gender-affirming hormones, and 66% of postmenopausal people reported breakthrough bleeding.”
It is not fully understood why the Covid vaccines can cause these changes to women’s menstrual cycles, but one theory is that the vaccines may trigger an immune response that can affect hormone levels. More research is needed to confirm this theory and to understand the long-term effects of the vaccines on women’s menstrual cycles.