'Plausible connection' between COVID-19 vaccine and period changes

Doctors say that even if the vaccine does have an impact on menstruation, it is short-term and the vaccine does not affect fertility.

 A woman suffers stomach pains or cramps (Illustrative) (photo credit: FLICKR)
A woman suffers stomach pains or cramps (Illustrative)
(photo credit: FLICKR)

Tens of thousands of women worldwide have reported changes in menstruation after receiving the COVID-19 vaccine, raising question marks among doctors and scientists.

Complaints have included changes to the duration and flow of their periods, and even pain, according to several surveys, but most doctors have stressed that there is just not enough evidence to directly link the jab to these changes.

Moreover, they say, the changes are short-term and there is no evidence that COVID-19 vaccination adversely affects fertility.

“We think that it is plausible there is a connection, but cannot prove this correlation,” said Dr. Itamar Netzer, an OB/GYN and medical administration specialist and a subdistrict director for Clalit Healthcare Services. “We are not much wiser” now than at the start of the vaccination campaign nearly 12 months ago.

Menstrual irregularities are a normal part of women’s lives, Netzer said. Women experience periods of irregularity throughout their fertile lifespan, sometimes brought on by bacterial or viral infections or even stress, though “most often for no reason at all.”

He said between 16% and 25% of women – normal, healthy and unvaccinated – experience irregular cycles, according to various studies. Around the same percentage reported menstrual changes as a result of COVID-19. An even smaller percentage of women expressed concern following vaccination.

 Navel of a woman (credit: Wikimedia Commons) Navel of a woman (credit: Wikimedia Commons)

EARLIER THIS month, during the live-streamed meeting of the Health Ministry’s Pandemic Response Team and members of its COVID-19 Vaccination Advisory Board, Dr. Emilia Ennis, director of the Health Ministry’s Department of Epidemiology, shared data collected by the ministry on the matter.

She noted that “all authorities in the world point out that the volume of reports that they have received on the subject is low in relation to the prevalence of such symptoms in the population regardless of the vaccine” – and that Israel is no different.

Ennis said the ministry received reports of heavy or unexpected menstrual bleeding, changes in menstrual periods and menstrual bleeding in women after menopause. According to the latest data she could provide, there had been 1,300 reports of these changes after the first dose out of two million women vaccinated and 2,000 reports after the second dose out of a million vaccinations.

“There is no way to know the prevalence [of these kinds of changes] in years past or to compare whether the prevalence is now higher, which may indicate a connection to the vaccine,” Ennis said. “Prolonged irregularity or excessive and unusual bleeding can be symptoms of other disease states, so if you experience an abnormal and prolonged phenomenon, especially if you are at risk for hypercoagulability or decreased platelets, consult your doctor.”

There are several reasons why COVID-19 vaccination could have short-term impact on a woman’s menstrual cycle, according to Israel Society of Obstetrics and Gynecology chairman Prof. Roni Maymon. He said this could include immunological influences on the hormones that drive the menstrual cycle or effects mediated by immune cells in the lining of the uterus.

In these cases, the effect would not be permanent but would disappear within two or three cycles.

The society announced in September that it would launch a comprehensive study on the subject, but two months later, according to Maymon, little progress has been made.

“First, we have to get ethical approval for the study [from the Helsinki Committee] and we have not even submitted it yet,” he said.

Maymon said that the study would be retrospective, meaning it would look at the medical records of a cohort of women.

Abroad, some studies have already been conducted or are in progress.


LAST WEEK, a paper uploaded to the health data sharing site MedRxiv – not peer-reviewed – stated that as of November 10, some 37,571 menstrual cycle changes had been reported to the United Kingdom’s Medicines and Healthcare products Regulatory Agency.

This particular study, however, only looked at 2,241 women over 18 who had at least one dose of any COVID-19 vaccine. They were asked to use a web-based form to report their age, length of normal menstrual cycle, whether they use any hormonal contraception, are breastfeeding, have ever been diagnosed with a menstrual or gynecological condition and, for each dose of the vaccine, which brand they had, on which day of their cycle they were vaccinated and details of how the timing and flow of their next period compared to what they normally experience.

The results showed that the brand of the vaccine was not associated with the period changes, meaning this phenomenon is not specific to mRNA vaccines. It also found that individuals taking hormonal contraception were more likely to experience menstrual changes after vaccination, but that vaccination timing was not directly related to the effect on the next period.

Dr. Victoria Male of the Department of Metabolism, Digestion and Reproduction at Imperial College London, who led the study, said that she has also recruited 250 women for a prospective study and that data collection from that cohort is still ongoing.

Last month, a larger survey of some 19,000 women was uploaded to MedRxiv, with more disturbing results: 42% of women with regular cycles said they bled more heavily than usual. Nearly a third experienced a longer duration of menstrual bleeding.

Moreover, among a cohort of women who do not typically menstruate, 71% were on long-acting reversible contraceptives, 39% on gender-affirming hormones, and 66% of post-menopausal women reported breakthrough bleeding.

This US study was led by researchers from Washington University in St. Louis, University of Illinois at Urbana-Champaign and Harvard University.

Netzer cautioned that the survey design used by the team asked women to “recall their experiences” and that there was no objective measurement for before and after being vaccinated.

A separate European study of about 16,000 women led researchers to conclude that “there is currently no evidence suggesting a causal relationship of menstrual disorders with Comirnaty,” the marketing name for Pfizer’s coronavirus vaccine.


REGARDING THE more than 30,000 reports of menstrual changes in the UK, the Royal College of Obstetricians and Gynecologists released the following statement by its vice president Dr. Jo Mountfield: “We understand that any changes to periods following a COVID-19 vaccine can be concerning. We want to reassure women that any changes generally revert back to normal after one or two cycles.

“There is no evidence to suggest that these temporary changes will have any impact on a person’s future fertility, or their ability to have children,” she continued. “It is important to get vaccinated as the best protection against coronavirus. This is especially important if you are planning a pregnancy, as we know unvaccinated pregnant women are more at risk of becoming seriously ill from COVID-19.”

Finally, the US National Institute of Child Health and Human Development awarded five grants totaling $1.67 million last month to agencies to explore the link between COVID-19 vaccination and menstruation changes, although this research has just started, and it is too early to report results.

The research teams are from Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University, and Oregon Health and Science University. The goal of their efforts is to see if the vaccine is directly linked to menstruation changes or if these changes are coincidental. They will also look at why these changes might occur and how long they might last.

Maymon said that there have been reports of reversible menstrual disturbances with other vaccines in the past, especially with the papilloma vaccination against a family of viruses that cause skin warts.

The US study published on MedRxiv also noted the link between other vaccines and period changes, including a study going back as far as 1913 that tied the typhoid vaccine with menstrual changes. They said studies of the Hepatitis B vaccine have also indicated that menstruation could be affected.

For Jewish religious women who observe the laws of family purity, these menstruation changes could be particularly challenging. However, Maymon said that once a conclusion about the phenomenon is made, “the rabbis will discuss with us and see what needs to be done according to Jewish law.”

In the meantime, stressed Netzer, “the most important thing to say is that we do know for certain that COVID-19 vaccinations do not affect fertility or pregnancy.

“In contrast, COVID-19 is very dangerous, especially for pregnant women.”