There are anecdotal reports that women’s menstrual cycles change after a COVID19 vaccine. These reports are on social media, in the VAERS system, and peppered throughout the mass media.
In short, women’s health may be indirectly related to the vaccine. This is what we know right now…
Some valid hypotheses are circulating
This is a sign the vaccine (and the immune system) is working. The strongest hypothesis is that the body is mounting an immune response and this is another transient side effect, like fever or body aches. The immune system is extremely complex and connected to every organ in the body, including the reproductive system (like hormones and sex organs). Vaccines may impact the signal (through estrogen production) between the brain (i.e. central nervous system) and lining of the uterus (i.e. reproductive system).
Stress and anxiety related to COVID-19 or getting vaccinated may be also linked (although, hopefully, this is followed by relief!). I, personally, hate when people say “oh you’re just stressed”, but stress is linked to health. Science on the relationship between stress and menstrual cycles, specifically, is less clear though.
Body temperature or disrupted sleep. We know the vaccine causes quite a few other immune responses (i.e. side effects), including fever or body aches (causing lack of sleep). Body temperature and lack of sleep have been scientifically linked to changes in menstrual cycles. So, if people are having vaccine side effects, it wouldn't be that unusual for some women to notice cycle changes too.
Could be random. Correlation does not indicate causation. Individually, it may be a sign that something else is going on that just coincidentally showed up after vaccination. On a population level, it may be due to something we call “recall bias”. Basically, in epidemiology we notice that when participants have an “event” they’re more likely to notice and report smaller details. We see this in cancer studies all the time. Cancer patients are more hyperaware of all the events leading up to cancer (because it’s a life altering diagnosis) compared to someone who never got cancer. So, people getting the vaccine could be hyperaware of changes compared to people that didn’t get the vaccine. This can cause a perceived imbalance.
Some invalid hypotheses are circulating
The vaccine is causing infertility. There is absolutely no data to support any impact on fertility or miscarriages from any COVID-19 vaccine. Here’s an older post of mine explaining the vaccine and infertility. But, Dr. Heather Huddleston (a OBGYN at University of California San Francisco OBGYN who specializes in reproductive endocrinology) said it best:
“This is a nuisance, it's troubling in that moment, but it's not a representation of something that's going to continue. It's not a representation of any sort of permanent harm or damage. There is no reason to think there's reason to be concerned over time, and there's no reason to think that there's any impact on fertility."
Spike protein is puncturing women’s reproductive organs. The spike on the actual antibody is incredibly, incredibly small. There is no biological way this tiny spike punctures the uterine lining and causes bleeding.
Viral shedding from the vaccine impacting health among unvaccinated women. There is no viral shedding from a vaccine. Shedding cannot happen without a live piece of coronavirus. And none of our vaccines contain the virus. (JJ and AstraZeneca do have a live virus but this is an adenovirus and cannot replicate). The vaccines also can’t give COVID-19. So, a person’s choice to get vaccinated has no negative (just positive) impact on an unvaccinated person’s health.
Are we seeing COVID-19 disease impact women’s health?
Yes, actually. Among a small study of 177 patients, 25% had menstrual volume changes: 20% had a lighter-than-usual period and 19% had a longer-than-usual cycle. While it's possible that the COVID-19 vaccine could have a similar effect, it's not known at this time. There has been no biological mechanisms proposed that would directly link the vaccine to menstrual volume.
This signal was not picked up during the clinical trial.
Why not? Well, unfortunately, there's a long history of us not doing a great job at studying women in research studies. Clinical trials, specifically, have not always adequately enrolled women or analyzed sex-specific differences in the data. This has hindered the progress of understanding women’s response to drugs or therapies or vaccines.
We’ve had progress among specific diseases that impact women (like breast cancer, cervical cancer, and heart health). But studying the impact of female biology on vaccines, drugs, or other disease areas (like depression and Alzheimer’s) remain suboptimal (and borderline unacceptable). There are national initiatives to improve this in research.
Nonetheless, this signal was not picked up during the COVID19 vaccine trials. This could because it’s random or (and more likely) it’s because data about menstrual cycles was just not systematically collected.
What should you do?
Don’t panic. This is likely a sign that your vaccine is working. Potential menstrual changes are typically short-term.
Talk to your healthcare provider. Sometimes when women experience heavy bleeding doctors can do a few tests, like a complete blood count.
Dr. Kate Clancy has a study to survey menstrual experiences post COVID-19 vaccination. To participate, click on the link here.