An American analysis is reassuring on the effects of the vaccine on the rules of women. A disturbance is sometimes observed, but only for one day on average.
Yes, vaccination can disrupt the menstrual cycle of women but this effect is limited, not serious and temporary, according to an American study published in the scientific journal Obstetrics & Gynecology Wednesday. The results “Are very reassuring”, said Alison Edelman, lead author of the study and professor of obstetrics and gynecology at Oregon Health & Science University. Right after receiving a Covid-19 vaccine, women’s menstrual cycles are lengthened by less than a day on average. The duration of the rules itself is not affected by the vaccination, according to this work carried out in the United States on nearly 4,000 women.
While a cycle usually lasts about twenty-eight days, this length varies from woman to woman, but also in a woman during 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
Fairly quickly after the start of the vaccination campaign, women testified to disturbances in their menstrual cycle after receiving the injection against Covid-19. Data closely monitored by health authorities. On July 30, the National Medicines Safety Agency (ANSM) reported in its pharmacovigilance investigation hundreds of cases observed following vaccination with Pfizer and Moderna. Files classified as “Potential signal” – therefore the subject of special attention. On September 24, a new update on these two vaccines confirmed the maintenance of this signal, without raising worrying situations or a proven direct link between vaccination and menstrual disorders. The ANSM then 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 aged 18 to 45, and not using contraception, informed about an application used to monitor menstrual cycles (for example to know her fertility periods). They compared the length of cycles of 2,400 vaccinated people – mostly with Pfizer (55%), but also with 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, an injection of vaccine was received during the fourth cycle. Results: there is indeed a lag in the menstrual cycle due to the vaccination, but which is on average less than a day (0.64 days). However, it is greater during the second dose (0.79 days). This lag became much more significant in women who received both doses in the same cycle (2.32 days difference on average). However, the duration returns to normal after two cycles.
A disruption of the “body clock”
“We know that the immune and reproductive systems are interconnected”, explains Alison Edelman, the study’s lead author. However, vaccines create a strong immune response. This response affects the hypothalamic-pituitary-ovarian axis, which the specialist describes as “The highway of communication between the brain, the ovaries and the uterus”.
This axis helps to regulate the menstrual cycle, which is why the researcher also gives it the nickname of“Body clock”. With vaccination, “You release proteins called cytokines, which we know from other diseases can disrupt this body clock”, she explains. The change also seems more pronounced when the vaccination is performed “Early in the follicular phase” (starting on the first day of menstruation and continuing until ovulation). In addition, the authors recall that“A severe acute illness such as Covid-19 can also be catastrophic for the function of the hypothalamic-pituitary-ovarian axis, sometimes permanently”.
Scientists hope to have gathered more data on subsequent cycles very soon to confirm this return to normal. This study has limitations since it relies 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 cycle lasts “Normal” and “Regular”. This makes it easier to see the effects of the vaccination and these results are reassuring.