Pfizer, AstraZeneca, and Moderna claim that the most common side effects of their COVID-19 vaccines are fever, fatigue, headache, body aches, and swelling. However, one of the more popularly discussed side effects of the COVID-19 vaccine among women in media and in clinics is menstrual dysregulation. Across the globe, women are complaining of periods of delay or early menstruation, heavier bleeding, increased dysmenorrhea, and breakthrough bleeding after receiving a dose of the COVID-19 vaccine3,9,10. On a physiological level, the menstrual cycle is tightly regulated by the hypothalamus-pituitary-ovarian axis. This axis is highly impacted by internal as well as external stimuli including social and psychological stressors.
Cortisol has been well established as a stress hormone that affects the reproductive organs, inflammation, and immune responses. Thus, it has been theorized that the psychological stress of vaccine skepticism coupled with the social stress of providing herd immunity to the vulnerable might increase cortisol secretion leading to sex hormones dysregulation and essentially menstrual disturbances post vaccine3,11.
With that in mind, we surveyed women to assess the extent of menstrual dysregulation post COVID-19 vaccine and identify the factors associated with that dysregulation. We found that among healthy women who had no doubts or misgivings about the vaccine, their menstrual cycle remained the same after the COVID-19 vaccine as it was before. Those women did not experience any changes in or new onset of regularity, volume, dysmenorrhea, or intermenstrual bleeding post vaccine. Their cycle was virtually intact. Not only that but 32 of them have also reported becoming pregnant after receiving the vaccine. Interestingly, this was not the case for vaccine skeptics.
Compared to the general population, women who are self-identified vaccine skeptics were 3 times more likely to report a change in their menstrual cycle including regularity, volume, and spotting. They perceived changes in 3 aspects out of 4; where non-skeptics perceived none. Of all skeptic women 64.71% reported no changes, 32.94% changed from regular to irregular, and 2.35% changed from irregular to regular.
Vaccine skepticism is currently an area of increased interest and ongoing research. It is so rampant that a team of psychologists in Romania developed a new scale to measure COVID-19 vaccine hesitancy12. Understanding the psychology of vaccine skepticism is somewhat challenging especially when most of these individuals are fully vaccinated and content with all vaccines except COVID-1913,14. By and large, women are reported to be less likely to consider vaccination as the only permanent solution to COVID-1914. Researchers argue that vaccine skepticism is largely due to lack of confidence in the vaccines’ effectiveness, concerns about unforeseen effects, belief in the existence of other solutions, the availability of effective medical treatment for the infected, fear of infertility, lack of full FDA approval, or that the vaccine is an altogether “big pharma” conspiracy15-19. All of aforementioned reasons can be attributed directly to misinformation and/or lack of proper effective communication from healthcare providers. Moreover, Hatmal et al7 found that vaccine hesitancy increases the likelihood of reported side effects that are not particularly limited to menstruation.
Other than vaccine skepticism, the only other group to report a change in volume was women on hormone-based contraceptives like OCP or IUD. Similarly, women with PCOS prior to receiving the vaccine were more likely to report a slight change in dysmenorrhea than those who did not have PCOS. These results are to be expected given that PCOS and contraceptives entail a fragile hormonal balance by definition. But even then, in spite of their exogenous hormone influence, the women’s reported changes were singular (only dysmenorrhea or only volume) rather than 3 at once. Having said that, COVID-19 vaccines appear to be significantly associated with disturbing the balance of people with a vulnerable hormone balance i.e. diagnosed PCOS or on a contraceptive. However, PCOS in and of itself is a risk factor for amenorrhea and dysmenorrhea so this might be a confounding rather than a result.
Of note, women who reported volume changes were split almost equally between the extreme opposites of the spectrum—normal to heavy and normal to scanty. Further, while some of them reported prolonged periods of delayed bleeding, others reported increased intermenstrual bleeding. In other words, there were no specific or predictable patterns to the claimed changes.
Originally, we hypothesized that oral period blocking pills might be associated with menstrual disturbances after receiving a COVID-19 vaccine dose; however, the results indicate that there is no relationship between the pills, the vaccine, or menstruation. Age does not appear to play a role either; nor does personal history of contracting the COVID-19 virus. Thus, the major associated factor for menstrual disturbances post COVID-19 vaccine was vaccine skepticism or having a preexisting hormonal imbalance before receiving any dose of the vaccine.
In this study, we did not ask about or account for body mass index (BMI) since previous research already had and they did not report any significant association between BMI, COVID-19 vaccine, and menstruation9. This paper can be utilized as a guide for future assessment studies of the COVID-19 vaccines and their perceived side effects among vaccine skeptics. Public education regarding vaccines is imperative to dispel the misinformation and clear the ambiguity surrounding COVID-19 and its vaccines.
Limitations
In the survey, we intentionally left out the question of whether the change was perceived or documented because we specifically wanted to see how vaccine skeptic women would answer. We believed that asking for proper documentation might skewer the results. That being said, we acknowledge that it might have led to an arbitrary answer resulting in self-reporting bias or recall bias20.