Vaccines against COVID-19 were developed and approved with unusual speed due to the serious situation caused by the pandemic, so their possible long-term side effects have been studied as they are identified in the population. In the case of women of childbearing age, many of them claimed to have experienced changes in their menstrual cycle, and there are also studies that have found that vaccination altered the menstrual cycle and had effects such as increasing its duration or the amount of bleeding.
Based on this information, the European Medicines Agency (EMA) included the presence of heavy menstrual bleeding as a possible side effect of messenger RNA vaccines – those of Pfizer / BioNTech and Moderna. However, a new investigation carried out by the Swedish Medicines Agency and the University of Gothenburg, in which the data of 2,946,448 Swedish women between the ages of 12 and 74 have been analyzed, has reached the conclusion that the incidence of menstrual disorders requiring medical attention did not increase after receiving mRNA vaccines from Pfizer (Comirnaty) or Moderna (Spikevax), or from AstraZeneca (Vaxzevria).
The study has been published in the BMJ journal and is one of the largest to date to assess the possible causal relationship between vaccination against SARS-CoV-2 and the appearance of menstrual disorders. The researchers followed these women between December 2020 and February 2022 and found no increased risk of menstrual disorders after vaccination, although they did see a slightly increased risk of medical consultation for postmenopausal bleeding.
There was no increased incidence of menstrual disorders after vaccination
The risk of menstrual disorders or bleeding after vaccination against the coronavirus was studied during two time windows: 1-7 days -considered the control period-, and 8-90 days, compared to the incidence among unvaccinated people. Factors that could affect the results, such as age, socioeconomic status, and need for prior care, were taken into account.
“What we have shown is that although the symptoms may have occurred and were bothersome to the woman, they have not been severe enough to prompt a visit to the doctor.”
87.6% of the women studied (2,580,007) received at least one vaccine against the coronavirus and 64% of those vaccinated received a total of three doses before the end of follow-up. “The greatest risks of bleeding in postmenopausal women were observed after the third dose, in the risk window of 1 to 7 days and in the risk window of 8 to 90 days.
Associations between SARS-CoV-2 vaccination and medical care requests for bleeding in postmenopausal women were weak and inconsistent, “and there was even less evidence of an association for menstrual disorders or bleeding in premenopausal women,” they have reported. The researchers wrote, adding: “These findings do not provide substantial support for a causal association between SARS-CoV-2 vaccination and healthcare contacts related to menstrual or bleeding disorders.”
Rickard Ljung, a professor and physician at the Swedish Medicines Agency and one of those responsible for the study, points out: “Our findings do not necessarily contradict reports that, based on self-reported data, showed a higher incidence of menstrual disorders after vaccination. . What we have shown is that although the symptoms may have occurred and were bothersome to the woman, they have not been severe enough to prompt a visit to the doctor.”
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