Do Covid-19 vaccines disrupt the menstrual cycle?

Last February, Dr. Kate Clancy, an American medical anthropologist, posted a tweet where she explained that she and a colleague had noticed that their periods were heavier than usual after receiving their first dose of Moderna vaccine against Covid. This tweet received more than 900 replies from women reporting problems with their cycles after receiving the injection.

A colleague told me she has heard from others that their periods were heavy post-vax. I'm curious whether other menstruators have noticed changes too? I'm a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I'm in my 20s again.

Testimonials without scientific value

Correlation or causation? Impossible to determine as it stands. After reading testimonials on the French-speaking Twitter, Numerama launched a fairly broad call for testimonials (“Notice to menstruating and vaccinated people: Have you noticed changes in your cycle after vaccination?”), We received 36 detailed responses from menstruating people who have noted disorders of their cycle.

Those who, because caregivers, have received their injection long enough to experience several cycles of menstruation testify to a return to normal thereafter.
If these testimonies are troubling, they have nothing to do with scientific value for several reasons. First, the sample is too thin. Then, because these are post-hoc observations (it would have been necessary to follow a large group of menstruating people before and after vaccination) and because there is no control group (it would also have been necessary to follow a group of unvaccinated menstruating people).

Finally, because it's purely declarative a posteriori: perhaps these people were more vigilant about their cycle than usual, perhaps they just asked themselves the question when reading the call to testimonies. Also, we don't know when in the cycle these people were vaccinated, whether they're taking hormonal contraception, and we don't know their history.

And then, precise methodological tools would be needed to objectively monitor the cycle with regular blood and urine hormonal assays as well as an evaluation of the flow which is done by sending periodic protections to the women who must then send them back to analysis purposes.

“Enough to freak you out a bit”

The fact remains that menstruating people wonder: “I was vaccinated (1st dose of Moderna) on May 11, I should have had my period on 17, and they arrived on the 23rd. It's not crazy, but enough to freak you out a bit. testifies Valérie, 40 years old.

Sandrine, 38, general practitioner, was also alarmed: “I was vaccinated very early at the end of January for the first dose of Pfizer as part of the vaccination of caregivers at risk of severe form. My period was supposed to come barely 2-3 days after the vaccine. This was not the case: I had spotting and what could be called meno-metrorrhagia (bleeding out of period) for more than a month (basically I had small bleeding daily)” , she tells us. “I went to consult my gynecologist who had an ultrasound and a biological assessment carried out (we feared either the onset of premenopause, or an ectopic pregnancy, or a problem with my IUD, or at worst a cancer of the uterus) . All examinations were normal. My gynecologist prescribed me progesterone treatment for two weeks, and everything was back to normal. And I had no problem when injecting the second dose. I raised the possibility of a disruption related to the vaccine, but at the time my gynecologist was not aware of this possibility. It must be said that we learn as we go along with this epidemic! »

Barbara, 46, was also consulted: "I haven't had a delay in the cycle, but since then everything is more exacerbated, my breasts are getting bigger and hurting me so much that I went to see my gynecologist. Everything was normal, just a variation in the physiology of the mammary glands as seen during the cycle. »

Source: Pexels

A lack of consideration of menstrual disorders

Faced with testimonies, one can ask the question not of the possible seriousness of these potential adverse effects in newly vaccinated menstruating people, but the fact that it does not show up in the results of phase 3 clinical trials.

Alexandre Regnault, lawyer at the Court and specialist in health and bioethics issues reminds us that “generally speaking, for years, there has been an under-representation of women in clinical trials. This was very voluntarily organized out of concern to protect the pregnant woman and the child from possible teratogenic effects. Today, it is more balanced even if there is perhaps an under-representation due to the need to take contraception during the clinical trial. However, verification made, menstruating people were equal in number with cisgender men in the studies, but perhaps the fact that they were on contraception could have played a role.

"Perhaps the question was not on the list of those asked of the participants in the trials", suggests the medical examiner and radiologist Franck Clarot. “Genito-sexual side effects in women are taken much less seriously than in men,” laments sexologist doctor Gilbert Bou Jaoudé. Indeed, as Professor Jean-Luc Squifflet, Deputy Head of Service in the Gynecology and Andrology Service at the Cliniques Universitaires Saint-Luc in Brussels, also points out: "The effect of a drug on the menstrual cycle is not never studied, except for hormonal treatments in gynecology”.

It therefore seems that the question of the modification of the menstrual cycle is not part of the undesirable effects sought for a vaccine since, as the gynecologist points out, "the abnormalities of the cycle are frequent, without there being any of pathology. “And no matter the stress caused and the fact that what seems to take precedence over the rest, for part of the medical profession, is that the person remains… able to give birth.

No pharmacovigilance signal

After phase 3 of a clinical trial comes phase 4 – the one in which the vaccines against Covid are currently on the market. During this period, pharmacovigilance makes it possible to refine the adverse effects of drugs in a large population. “There is no pharmacovigilance signal concerning menstrual cycle disorders. ” tells us Mathieu Molimard, head of the medical pharmacology department at the Bordeaux University Hospital.

Stéphane Korsia-Meffre, medical writer, teacher in the University Department of General and Veterinary Medicine confirms: “These disturbances in the cycle are not a strong signal or not a sufficiently intense signal for it to appear in the pharmacovigilance data. » Women, accustomed to hiding their menstrual inconveniences, have they thought to report it? Did they think of them as newsworthy enough?

What do you think of all this today? First, that if there are menstrual cycle disorders linked to vaccination, they are not serious, and that vaccination has no impact on fertility in any way: "It's fake news, that to say that the vaccine makes you sterile. Insofar as a vaccine reproduces in less strength and in benign what a virus can do, the pandemic would have rendered sterile a good part of the women who contracted it, but this is not the case, ”insists Mathieu Molimard. . “This rumor comes from an experiment where we injected very large doses of vaccines into rats – doses that are not injected into humans. »

In fact, in no case, and insofar as these abnormalities of the cycle are benign and transient, these testimonies should not divert women from vaccination against Covid-19.

Correlation is not causation

Next, we cannot speak of a causal relationship until a serious clinical study has been conducted. "In my opinion, it will be difficult to estimate without a real prospective study the impact of vaccines against Covid on the menstrual cycle" believes Gilbert Bou Jaoudé, "because on the one hand, people who notice changes in their cycle do not necessarily make the link with vaccine and on the other hand, there are so many factors which can modify a cycle that it will be difficult to relate to the vaccine. »

As Jean-Luc Squifflet reminds us, "many things can influence the cycle, whether it's the state of health (infection, dialysis, obesity, anorexia, etc.) or external factors (emotional shock, stress, etc.)" what it is possible to do today is to put forward hypotheses while remaining reassuring. “There could be a disruption of the cycle when the immune response caused significant adverse effects with fever, thus mimicking an infection. postulates Jean-Luc Squifflet.

"We know that any state of stress in the physiological sense can cause disturbances in the menstrual cycle," says Gilbert Bou Jaoudé. “However, vaccination could cause a state of stress in the body linked to the activation of the immune system. It is therefore not illogical to hear such complaints (…) It is possible that these signals subsequently justify a study and we can then discuss the consequences if the disorders of the cycle are found documented and if a causal link between the vaccine and cycle disruption turns out. »

The consequences? Certainly not a withdrawal from the market or a suspension of vaccination for menstruating people, but more information and transparency which will make it possible to put at a distance the far-fetched conjectures of antivax based on testimonies.

If, however, you experience cycle disorders after vaccination, do not hesitate to report them on the ANSM website.

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