New study confirms: COVID vaccine linked to menstrual irregularities

Jan 11, 2022


09:38 AM

What prompted the study? 'Concerns about vaccine hesitancy'

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By September, 2021, over 30,000 reports of menstrual irregularities following COVID-19 vaccination had been registered by the UK’s Medicines and Healthcare Products Regulatory Agency (MHRA), the near-equivalent of the VAERS system. Now a new study has confirmed that COVID-19 vaccination is linked to changes in the menstrual cycle; the implications for fertility are as yet unknown.

What prompted this study? No mere healthy scientific curiosity and not even concern that the vaccine may truly have deleterious effects on female fertility; the preamble to the study makes it clear that “concerns about a possible association between coronavirus disease 2019 (COVID-19) vaccination and abnormal menstrual cycles [that] may lead to vaccine hesitancy” were the motivating factor (emphasis added). 

This was not the first study to examine menstrual irregularities; back in 2021, a study conducted by a number of scientists examining British data also concluded that vaccination was linked to menstrual irregularities, with 1 in 5 of the almost 5,000 study participants reporting that vaccination had caused disturbances. The report added that, “This study was conducted before the widespread media attention to menstrual changes related to COVID-19 vaccination.”

The study’s authors also noted that according to “a recent preprint of a retrospective case-control study of 21,380 pre-menopausal participants living in the U.S., 45.8% of 9,579 people with regular menstrual cycles experienced heavier bleeding after COVID-19 vaccination. In addition, 70.5% of 1,545 non-menstruating people using long-acting reversible contraceptives (LARC) experienced breakthrough bleeding after COVID-19 vaccination.”

As evidence of irregularities associated with vaccination mounted, however, many in the medical establishment doubled down and continued to insist that there was nothing to worry about. An editorial published in The British Medical Journal in September, 2021, for instance, stated categorically that “there is no evidence that Covid-19 vaccination adversely affects fertility” – based on the fact that in clinical trials, “unintended pregnancies occurred at similar rates in vaccinated and unvaccinated groups.” The author added that menstrual changes are also associated with “immune activation in response to various stimuli, including viral infection,” and that “vaccination against human papillomavirus (HPV) has also been associated with menstrual changes.”

The HPV vaccine has indeed been associated with menstrual changes, and also with premature ovarian insufficiency. But most vaccines are not, and the fact that the HPV vaccine was associated with such a serious condition is hardly reassuring. 

But “association” is not the same as “causation,” enabling many medical professionals to claim, as one doctor among many did in response to the huge number of complaints, that. “There have been lots of anecdotal reports … [but] it is very difficult to know if these changes are a direct effect of the vaccine itself or are due to wider effects of the pandemic.” 

With the latest study, however, a link seems far more certain. Almost 4,000 women were enrolled in the trial; 2,403 were vaccinated during the course of the study and 1,556 were not. This study focused on the effects of mRNA vaccines (55 percent of women received the Pfizer vaccine, 35 percent the Moderna vaccine, and just 7 percent the Janssen vaccine). The authors concluded that: 

“Overall, Covid-19 vaccine was associated with a less than 1-day change in cycle length for both vaccine-dose cycles compared with pre-vaccine cycles (first dose 0.71 day-increase, 98.75% CI 0.47-0.94; second dose 0.91, 98.75% CI 0.63-1.19); unvaccinated individuals saw no significant change compared with three baseline cycles… Change in menses length was not associated with vaccination.”


“A subset of individuals who received both vaccine doses in a single cycle [that is to say, within the space of five weeks or less] had, on average, an adjusted 2-day increase in their vaccination cycle length compared with unvaccinated individuals. Although approximately 10% of these individuals experienced a clinically notable change in cycle length of 8 days or more, this change attenuated quickly within two postvaccine cycles.”

Following the earlier trial, researchers claimed that any effect, if truly caused by the vaccine, passed quickly; this time the trial’s authors admitted that, “our data do not yet include enough subsequent cycles without vaccine to investigate this fully.” 

But this time, again, researchers found the trial’s results “reassuring” as they were not “clinically meaningful.” And this time, again, they stressed that any “acute severe illness with or without septicemia, such as COVID-19, could be catastrophic to hypothalamic-pituitary-ovarian axis function, sometimes permanently.”

In fact, their conclusion was that it was likely the “robust immune response or stressor” that was responsible for the irregularities noted, and that women should not hesitate to use what is clearly a highly effective vaccine product.

The BMJ was more categorical in its general dismissal of concerns: “Vaccine hesitancy among young women is largely driven by false claims that Covid-19 vaccines could harm their chances of future pregnancy.” But is a claim that a vaccine “could harm” fertility really false? 

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