Could the mRNA COVID-19 vaccines change women’s menstrual cycles?
A new French study has found evidence that they might while some experts caution that other factors could also be at play.
The research “provides new arguments in favour of the existence of an increased risk of heavy menstrual bleeding following vaccination against COVID-19 by mRNA vaccine,” according to a statement from Epi-Phare, an organisation that carries out national health studies for the French government.
The researchers documented the vaccination status of around 4,600 women admitted to hospitals due to significant menstrual bleeding in 2021 and 2022.
They compared their condition to a control group of women who were not treated for this issue.
Their findings suggest that the risk of experiencing heavy menstrual bleeding is marginally higher after a woman receives her first Moderna or Pfizer vaccine, both administered in two consecutive doses.
This increased risk continued for one to three months after vaccination. There was no observed risk of heavy menstrual bleeding after a subsequent booster dose.
“It's important to hear what women have to say,” Dr Odile Bagot, a gynaecologist who didn’t take part in the study, told Euronews Next.
“If there is a causal relationship, it's neither very frequent nor very significant in the end, and it's certainly not persistent beyond three months,” she added, regarding the study’s outcome.
No scientific consensus
Since initial reports of changes to women’s menstruation cycles post-vaccination, several studies have been conducted to determine if that’s the case..
A study published in January 2024, which analysed data from users of a period tracker application, concluded that vaccination was “associated with a small change in cycle length” that “resolves quickly within the next cycle”.
Another study drew similar conclusions. Conducted on the Swedish population and published in May 2023 in the British Medical Journal (BMJ), it stated that the “findings do not provide substantial support for a causal association between SARS-CoV-2 vaccination” and menstrual disorders reported to health professionals.
“When you have contradictory studies. It doesn't mean that one is lying and the other isn't, it means that the phenomenon is far from certain and not very strong,” Bagot said.
Other factors could also have played a part in menstrual changes.
“Both the stress of vaccination and the inflammatory and immune phenomena that necessarily follow vaccination can influence the cycle,” added Bagot.
