Among the side effects of the COVID-19 vaccines, their influence on menstruation has been pointed out and, in fact, a study carried out by researchers from the National Institutes of Health (NIH) of the United States found that these drugs, especially the vaccines from Pfizer-BioNTech and Moderna – which are of the mRNA type – could increase the duration of the menstrual cycle by an average of one day.
Another study published in the British Medical Journal (BMJ) concluded that the alterations were mild and short-lived. Now, new research with more than 39,000 participants (including women and gender-diverse people) led by Tulane and Illinois University anthropology professors Katharine Lee and Kathryn Clancy reveals that 42% of menstruating women experienced an increase in the flow of their menstruation after receiving the SARS-CoV-2 vaccine. Their results have been published in Science Advances.
In addition, and for the first time, the appearance of spontaneous bleeding is also described in a high percentage of non-menstruating people, who did not have their period because they had reached menopause, or because they were following hormonal contraceptive and transgender treatments. Among the people surveyed, 42% of those who had regular menstrual cycles bled more than normal, while 44% experienced no change after being vaccinated. Among respondents who do not normally menstruate, 71% of those taking long-acting reversible contraceptives, 39% of those taking gender-affirming hormones, and 66% of postmenopausal women reported having breakthrough bleeding.
The results of this observational study –one of those with the largest number of participants to date– indicate that the alterations observed would be temporary and that among the factors that most influence their appearance are age, having suffered systemic side effects associated with vaccination (fever or fatigue), pregnancy and childbirth history, and ethnicity, among others.
“In no case should such research feed anti-vaccine theories, but serve to confirm the need for this and other side effects not to be overlooked again in clinical trials”
Dr. Ana Beatriz Rodríguez Moratinos, Professor of Physiology at the University of Extremadura (UEx), and Dr. Cristina Carrasco, postdoctoral researcher, both from the Neuroimmunophysiology and Chrononutrition group of the UEx and co-authors of a similar study in Spain, in statements to SMC Spain, they have said: “When the rumor about the appearance of alterations in the menstrual cycle after receiving the COVID-19 vaccine became a clamor on global social networks, researchers such as the North Americans Dr. Lee and Dr. Clancy, from the Department of Anthropology of the University of Illinois (USA) took an important scientific step in the pandemic, launching an observational study that would allow dispelling doubts about a phenomenon that they themselves had suffered.
Impact of anti-COVID vaccines on the menstrual cycle
This research confirms a phenomenon that has been talked about since the vaccination campaigns began and that will undoubtedly help to clarify in the coming months the scientific evidence that similar studies have found, including those that are being carried out in countries with high rates of vaccination in its population, such as Spain.
“Menstruating and previously menstruating people began sharing that they experienced unexpected bleeding after they were given the COVID-19 vaccine in early 2021,” the authors explained, stating that due to limited data Previously available vaccines against COVID-19 have not been considered a stressor with a potential impact on the menstrual cycle, which once again highlights the lack of consideration and knowledge about an aspect that is of key importance in women’s health.
“Although menstrual disorders are not uncommon and dangerous, the evidence provided by this and other studies will allow, in the future, to elucidate the inflammatory mechanisms, and we would dare to say that also oxidative, underlying this emerging phenomenon. From our point of view, in no case should such research feed anti-vaccine theories, but serve to confirm the need for this and other side effects not to be overlooked again in clinical trials. Likewise, such evidence will provide health professionals with a greater capacity to assess their patients through information validated by science”, conclude the UEx researchers.
.
