The most comprehensive analysis of menstrual changes following a Covid-19 vaccination has revealed that its recipients experienced pre- and postmenopausal changes in the first two weeks following vaccination.
After receiving the vaccine in early 2021, a significant number of menstruating or formerly menstruating people began experiencing unexpected bleeding. Many of these cases were considered anecdotal, but slowly a pattern emerged.
Changes in menstruation are not unheard of when it comes to vaccines. Other vaccines such as those for HPV, Hepatitis B, and typhoid have also been linked to changes in menstruation. This side effect is believed to have less to do with hormonal changes and more to do with elevated immune-related inflammatory pathways. Researchers suspect that these changes are only temporary.
In April of 2021, the study team surveyed over 35,000 people regarding their experiences after vaccination. The survey questions included information on demographics and other things but also focused on reproductive history and menstrual bleeding.
On June 29th, 2021, the researchers retrieved the survey data. Because menstrual changes have also been linked to Covid-19 infection, those who had the virus were not included in the analysis. People 45-55 years of age were also excluded to avoid confusion about menstrual changes related to perimenopause.
The analysis specifically focused on those who menstruate regularly, and those who have menstruated in the past but do not do so currently. This included postmenopausal individuals and those suppressing menstruation through hormonal therapies for whom bleeding would be highly unlikely.
The researchers reported that 42.1% of the respondents were revealed to have had a heavier menstrual flow following vaccination. For some, these changes happened within the first seven days after vaccination, but for the majority, changes occurred 8-14 days following vaccination. On the other hand, 43.6% of the respondents reported no change in menstrual flow, while only 14.3% noticed a mix of lighter flow to no change in flow.
However, the study was reliant on experiences that were self-reported and logged more than 14 days after the vaccination. Because of this, the researchers could not establish causality, and the study cannot be considered a reliable predictor of the general population. It can, however, be used to identify potential associations between an individual's demographics, reproductive history, hormonal status, and menstrual changes after vaccination.
For example, participants were more likely to report heavier bleeding following vaccination after having experienced pregnancy, while those who had yet to give birth experienced only a slight increase.
After receiving the vaccine, most non-menstruating premenopausal respondents on hormonal treatment experienced bleeding. Over 70% of the respondents who used long-acting reversible contraception, along with another 38.5% undergoing hormone treatments for gender-affirmation, also claimed to have had this side effect.
Respondents who identified as non-white, Hispanic/Latinx, were older, or experienced fever or fatigue after vaccination were more likely to have had a heavier menstrual flow as a side effect than other groups who had received the Covid-19 vaccine. Others with reproductive disorders such as menorrhagia, fibroids, endometriosis, among others were also more likely to have experienced heavier menstrual flow post-vaccination.
Though an increase in menstrual flow can be only temporary in some people, these changes, nonetheless, can be alarming.
Breakthrough bleeding in postmenopausal individuals and those using gender-affirming hormones could be an early warning sign of some cancers. This unexpected experience can lead one to worry and seek out procedures for cancer screening that can be invasive and expensive.
When it comes to the early diagnosis of cancer, screenings are essential. It would also be helpful for diagnostic purposes to know if there are other underlying causes for the bleeding. But anyone who experiences breakthrough bleeding should see a doctor.
Menstruation is a natural and expected part of life that can be affected by all kinds of stressors. And a change in bleeding patterns can be noticeable, but the reason for the change is not always apparent. In the future, it would be helpful to include questions regarding menstruation in vaccine testing beyond those referring to pregnancy. Information such as this could possibly prevent unnecessary worry and the expensive and invasive screenings that come with detecting cancers.
Sources: Science, University of Illinois, PLOS
