Vaccination and Covid-19: Is there a hormonal disorder?

This is a very targeted but very unpleasant side effect: delayed periods, modified or more painful flows, bleeding in postmenopausal women…

For several months, testimonies of people experiencing menstrual cycle disorders following the injection of one or more doses of mRNA vaccine against covid-19 abound on social networks, but not only To date, what is known about the occurrence of these menstrual disorders during a pandemic?

Here is a review of the press, scientific studies, and pharmacovigilance data available 24 February 2021, the alerts were launched on Twitter by the American medical anthropologist Kate Clancy: after receiving a dose of Moderna vaccine, she noticed that her periods were abnormally heavy. Hundreds of similar reactions and testimonials followed in response to her tweet.

A few months later, in May 2021, Passeport Santé took up the subject and relayed this other astonishment from Victoria Male, a reproductive immunologist at Imperial College London In August, Franceinfo took an interest in these multiple alerts, but this time from the angle of “True or False”: “What is it really? In August, it was Franceinfo’s turn to look at these multiple alerts, but this time under the angle “True or false”: “What is it really? Where we learn that the National Agency for the Safety of Medicines and Health Products (ANSM), which ensures, in particular, the pharmacovigilance on the anti-Covid vaccines, has identified for the first time on July 30, 2021 “a ‘potential signal behind the reported cases of post-injection menstrual disorders (…) and not a formally established link”. If the Agency did not wish to respond to the requests of Franceinfo”, it specifies in its explanatory note that these effects are “mostly not serious”. Across the Channel, Francinfo continues, no less than 27,501 reports – out of 43.4 million people vaccinated – have been collected by the English counterpart of the ASNM.

The cause was “heavier than usual periods, delayed periods or unexpected vaginal bleeding”. How bad is it, doctor? For Jacky Nizard, According to the gynecologist-obstetrician interviewed for the occasion, these “anomalies are minimal”. He adds that these are not serious complications, which bring women to the emergency room”. Note that, since then, the ASNM has nevertheless added menstrual disorders to the list of potential adverse effects to the anti-Covid vaccines)”, indicated France Bleu. 


A new update on the situation, on December 21, 2021: to date, reports Le Monde, the ANSM reaffirms that despite a “significant number of notifications” received, “the available data do not make it possible to determine a direct link between the vaccine and the occurrence (of menstrual disturbances). Clearly, there is still nothing to worry about, since the majority of these events are “non-serious, short-lived and self-limiting”.

The same sound of the bell comes from the European Medicines Agency, informs France Bleu. But for one of its officials, Georgy Genov, this lack of direct link does not take away from the “need” to carry out additional studies on the subject, including “measurements of hormone concentrations” the same paper mentions the study unveiled the same day by the Norwegian Institute of Public Health: carried out on 6,000 women aged between 18 and 30, it reveals that “menstrual cycle disorders are more frequent after vaccination”.

As these results have not yet been submitted to peer review, the authors emphasize that they “must be confirmed by other studies”. … THEN AMERICAN We have to wait until January 05, 2022, and the publication of an American study financed by the National Institutes of Health (NIH) in the scientific journal Obstetrics & Gynecology, to know more. From the newspaper Sciences et Avenir, all share this information sent by AFP: “Vaccination can disrupt the menstrual cycle but without real seriousness”, was the headline in Libération on January 7th. As indicated by The Huffington Post, scientists have studied the length of the cycles of 2403 vaccinated women – mostly with Pfizer (55%), but also with Moderna (35%) and Johnson & Johnson (7%) -, aged 18 to 45 years and not using any contraception. To do this, they analyzed the data they entered on Natural Cycle, an application validated by the U.S. Drug Administration and used to monitor their cycle. They then compared it with data from a control group of 1556 unvaccinated individuals.

The most notable results concerned the lengthening of the menstrual cycle of vaccinated individuals: “An increase in duration was indeed observed in the vaccinated group (editor’s note: after administration of a first dose), but by less than one day (0.64 days). Following the second injection, the length of the menstrual cycle was extended by an average of 0.79 days. As for the duration of menstruation before and after the injection, it remained unchanged.

These results are “very reassuring”, says Alison Edelman, professor of obstetrics and gynecology at Oregon Health & Science University and principal author of the study. She also says that part of the reason for the change is that the immune and reproductive systems are interconnected. And, since vaccines cause a strong immune response, it is the “body clock”, responsible for regulating the menstrual cycle, that is affected. Clearly, it is the immune response to the vaccine, rather than the vaccine itself, that is the cause of these disorders.



On January 10, 2022, it was the turn of the media Numerama to relay the conclusions of the study. While it immediately points out that the findings “largely support the vaccination of menstruating people”, it also points out that all the disturbances of the menstrual cycle suffered by women are not fully elucidated”. Thus, “exacerbated menstrual symptoms”, “menstrual There are no data on “unexpected bleeding” or “qualitative and quantitative changes in the flow”. Especially since this is not the first time that a vaccine has caused hormonal disorders: “In 1913, it was shown that vaccination against typhoid was associated with irregularities in the menstrual cycle,” says an article in the blog Réalités Biomédicales (Le Monde), run by the doctor Marc Gozlan.

The same is true for vaccination against hepatitis B or papillomavirus (HPV). The problem, notes the author, is that the follow-up of vaccine clinical trials “does not usually include the search for irregularities in the menstrual cycle or bleeding, which makes it difficult to determine whether these changes are a coincidence or a potential side effect of the vaccines. Therefore, he says, “clear and transparent information about these possible effects” should be provided.

In the absence of such information, rumors are rife in the so-called “This is the case for the theory that vaccination harms the fertility of women and men, a theory that has been largely invalidated by the scientific community. Not to mention the strong social dimension of this issue related to women’s health. Therefore, still in Numerama, the journalist invites to question more the “disruptions of the cycle in this period of pandemic (…) otherwise women could again suffer gender inequalities”. As revealed by Courrier International, the stress induced by the Covid-19 pandemic would indeed have led to other “disruptions” of their menstrual cycle: with, again, “early or delayed periods, (more) pronounced symptoms or [more] heavy bleeding”.

The study, published in the journal Fertility and Sterility, concludes: “These changes may affect women’s well-being, especially for those who are trying to have a child. This study shows that the subject goes far beyond informing women about the possible side effects of a particular vaccine but should push medical research and society as a whole to take women’s health more seriously.

In December 2021, The International Journal of Epidemiology already sounded the alarm: “The lack of high-quality research on Covid-19 and the menstrual cycle reflects the broader focus of medical research, which does not prioritize women’s health, especially outside the context of pregnancy. The finding that menstrual cycles appear to have been affected by the Covid-19 pandemic could have important implications for society, gender-based inequalities, and post-Covid economic recovery.” In short, for women, it’s a bit of a double whammy.

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