Covid-19: Vaccination May Alter Menstrual Cycle But It’s Not Really Serious, Study Finds

The Covid-19 pandemic in Francedossier

An American analysis is reassuring about the effects of the vaccine on women’s periods. Sometimes a disturbance is observed, but only for one day on average.

Yes, vaccination can alter the menstrual cycle of women, but this effect is limited, not serious and temporary, according to a US study published Wednesday in the scientific journal Obstetrics & Gynecology. The results “are very reassuring,” said Alison Edelman, lead author of the study and a professor of obstetrics and gynecology at Oregon Health and Sciences University. Immediately after receiving a COVID-19 vaccine, women’s menstrual cycles last less than a day on average. The duration of the rules themselves is not affected by vaccination, according to this study carried out in the United States on about 4,000 women.

Although a cycle usually lasts about 28 days, this duration varies from one woman to another, but also in a woman throughout her life. The duration can, for example, vary during periods of stress. Any change of less than eight days is classified as “normal” by the International Federation of Gynecology and Obstetrics.

Particular attention

Quite quickly after the start of the vaccination campaign, the women testified to alterations in their menstrual cycle after receiving the Covid-19 injection. Data closely monitored by health authorities. On July 30, the National Agency for Drug Safety (ANSM) reported in its pharmacovigilance investigation hundreds of cases observed after vaccination with Pfizer and Moderna. Files classified as “potential signal” – therefore the subject of special attention. On September 24, a new update of these two vaccines confirmed the maintenance of this signal, without raising worrisome situations or a proven direct link between vaccination and menstrual disorders. The ANSM later indicated that there was no data to establish a real link between the bites and these disturbances.

To answer these questions, the American researchers used data from women ages 18 to 45 who were not using contraception, reported on an application used to monitor menstrual cycles (for example, to find out their fertility periods). They compared the cycle lengths of 2,400 vaccinated people, mostly with Pfizer (55%), but also Moderna (35%) and Johnson & Johnson (7%), with those of 1,500 unvaccinated women.

Six consecutive cycles were studied for all participants, but for the first group, a vaccine injection was received during the fourth cycle. Results: there is a delay in the menstrual cycle due to vaccination, but on average it is less than one day (0.64 days). However, it is higher during the second dose (0.79 days). This delay became much more significant in women who received both doses in the same cycle (2.32 days apart on average). However, the duration returns to normal after two cycles.

A disruption of the “biological clock”

“We know that the immune and reproductive systems are interconnected,” says Alison Edelman, lead author of the study. However, vaccines create a strong immune response. This response affects the hypothalamic-pituitary-ovarian axis, which the specialist describes as “the communication pathway between the brain, the ovaries and the uterus.”

This axis helps regulate the menstrual cycle, which is why the researcher also gives it the nickname “body clock.” With vaccination, “proteins called cytokines are released, which we know from other diseases can alter this biological clock,” he explains. The change also appears to be more pronounced when vaccination is done “early in the follicular phase” (from the first day of menstruation to ovulation). In addition, the authors recall that “a serious acute disease such as Covid-19 can also be catastrophic for the function of the hypothalamic-pituitary-ovarian axis, sometimes permanently”.

Scientists hope to have collected more data on subsequent cycles very soon to confirm this return to normal. This study has limitations since it is based on the users of these applications, who are not necessarily representative of the population. In addition, the researchers limited themselves to data from women whose cycles are “normal” and “regular” in length. This makes the effects of vaccination easier to see and these results are reassuring.


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