(Paris) It is very difficult to establish a link between anti-COVID-19 vaccines and the occurrence of major menstrual disorders, concludes Thursday one of the largest studies to date on a subject that has been the subject of many questions since. the start of vaccination campaigns.

There is no “strong basis for a causal link between vaccination against SARS CoV-2 and consulting for a menstrual disorder or bleeding”, conclude the authors of this study published in the British Medical Journal (BMJ).

This work was based on the health data of some three million Swedish women, or 40% of the female population of the country, which makes it a study of a rare scale on a subject which still lacks clear-cut answers.

Since the start of the anti-COVID-19 vaccination campaigns almost two and a half years ago, many women have reported disruptions in their menstrual cycles.

Based on these statements, the European Medicines Agency (EMA) notably ended up including the presence of heavy menstrual bleeding as a possible side effect of messenger RNA vaccines, those from Pfizer/BioNTech and Moderna.

Nevertheless, these are disorders declared individually by the patients. However, menstrual disorders can come from a multitude of factors and the course of the rules is very variable from one woman to another.

The BMJ study is therefore one of the first large-scale studies that try to clarify the likelihood of a causal link between vaccination and menstrual disorders.

She’s not going that way. Among women of menstruating age, there is no clear link between having been vaccinated – by Pfizer/BioNTech, Moderna or AstraZeneca – and having subsequently consulted a healthcare professional for a bleeding disorder. menstrual cycle.

However, these results are based on the fact of having requested such a consultation. They cannot therefore account for menstrual disorders that would not have given rise to contact with a caregiver.

“What we show is that if there are disorders, they do not seem serious enough for women to seek medical attention,” Rickard Ljung, one of the main authors of the report, told AFP. the study.

In addition, in postmenopausal women, the study establishes a slight association between vaccination and the fact of having consulted for bleeding.

However, this association is “weak and not uniform” and, in detail, does not necessarily correspond to the hypothesis of a cause and effect link, judge the researchers.