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Covid vaccine disturbs menstruation for some women, finds French study

Health body claims risk of very heavy bleeding slightly increased in the three months following the first mRNA Covid vaccination

A view of a woman in a hospital gown sitting on an examination bed

Women who had received their first Covid vaccination in the past one to three months had a higher risk of being hospitalised with heavy bleeding, the study showed Pic: Rocketclips, Inc. / Shutterstock

The Covid vaccine caused menstruation problems for some women, a new French study has found - but the medical community has still not reached a consensus on the issue.

Health authority Epi-Phare (the French medicines safety authority and the Sécurité Sociale) released a study, on January 24, stating that the risk of very heavy bleeding slightly increased in the three months following the first mRNA Covid vaccination.

The main mRNA vaccines used were those from Pfizer/BioNTech and Moderna.

In the study, researchers recorded the vaccination status of 4,610 “non-pregnant or postpartum” women aged between 15 and 50 - with no history of hysterectomy or coagulation disorders - who were hospitalised in France between May 12, 2021 and August 31, 2022 for heavy menstrual bleeding.

They compared them to a control group of 89,375 women who had not been admitted for this reason. The control patients were matched for the same characteristics of age, place of residence and contraceptive use.

At the time of the study, 71% of cases and 70% of controls had received at least one dose of vaccine against Covid during the past one to three months.

The study concluded that the risk of such a menstrual condition was slightly higher after the first Moderna or Pfizer vaccine - which was administered in two successive doses (one vaccine followed by another a few weeks later). The risk was found to last for three months, and would then disappear, even after subsequent booster doses.

The risk was “not increased for women whose last dose was a primary vaccination dose given more than 3 months previously or a booster dose”, the study said.

It comes after significant numbers of women complained of menstrual disturbances after having received their vaccine for the first time. This led the European Medicines Agency (EMA) to include ‘heavy menstrual bleeding’ as a possible side effect of these vaccines.

Lack of consensus

However, scientists so far do not appear to have reached a consensus on the issue, with one major study from Sweden contradicting the Epi-Phare study. 

The report, published in the BMJ (British Medical Journal) in 2023, said that there was no solid evidence of a link between these Covid vaccinations and subsequent menstrual disorders.

However, when asked by AFP about the lack of consensus, Epi-Phare said that the differing conclusions were the result of differing methodology. It pointed out that the Swedish study “took into account a risk period which began just over a week after patients had been vaccinated”. 

This “may have masked a possible increase in risk occurring a little later”, said epidemiologist Dr Rosemary Dray-Spira, who supervised the French study.

In contrast to the Swedish method, the French study waited until a month after the first dose of vaccine to begin studying the patients affected.

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