Hallelujah — a vaccine! Thanks to the sleepless nights and endless hard work performed by scientists, normalcy is right around the bend, right? For those who are vaccinated (or have even received a flu shot), we all know of the symptoms they warn you about: fever, soreness, fatigue, even headache. But have you noticed anything different with your period? Concrete data is limited, but there have been some reports of menstrual irregularities following the vaccine. 

According to Dr. Jen Gunter, an OB-GYN and best-selling medical author specializing in chronic pain and vulvovaginal disorders, vaccine trials historically have very limited data regarding menstruation patterns, and it’s becoming a point of concern that we don’t track that data. Did someone say #menstrualequity? Tracking menstrual irregularities should be just as crucial as tracking fevers, headaches, or nausea following a vaccine and even in the trial stages. It’s not that menstrual irregularities mean something is biologically wrong post-vaccine, it’s just that people should be warned of side effects that aren’t just applicable to both people with or without periods. 

You may be thinking, but what do periods have to do with COVID-19? Menstrual and sexual health are still major components of a persons’ holistic health — so it’s a little strange that real-time menstrual bleeding patterns aren’t even measured in STI-preventative vaccines, such as Gardasil.

What do I mean by “real-time?” In some vaccine studies unrelated to COVID-19, menstrual bleeding patterns have been tracked retrospectively, meaning patients are asked if they can remember their experiences. Recall bias may occur and offset data to be inaccurate — rather than if menstrual bleeding patterns were measured in real-time. However, just to cover our bases, please note that there has been no link identified between the HPV vaccine and infertility or miscarriage.

"There's a long history of us not doing a great job at studying women in research studies because of some of this complexity," said University of California, San Francisco OB/GYN, Dr. Heather Huddleston, who specializes in reproductive endocrinology.

Although menstrual cycles can be affected by a multitude of factors, health care professionals such as Dr. Huddleston agree that there seems to be a disconnect when it comes to tracking menstrual irregularities in the early stages of clinical trials. But similar to a sore arm, fatigue, or nausea, it’s a side effect that should be tracked so patients aren’t surprised.

so why & how would the COVID-19 vaccine mess with your period?

Menstrual bleeding can be offset by a plethora of factors — vaccine or not. The COVID-19 vaccine could potentially affect menstruation due to the impact on the chemical messaging from the brain to the ovaries, the ovaries to the uterus, or may directly affect the lining of the uterus — causing an earlier, heavier, or more crampy period than usual.

These effects could derive from the vaccine itself, the immune system response to the vaccine, or potentially related to vaccine symptoms, such as a fever or even stress. 

Additionally, in late April of 2021, Dr. Akshat Jain, a hematologist at Loma Linda University School of Medicine, who specializes in bleeding disorders in adolescent women explained that the vaccine could trigger inflammatory cells, therefore affecting hormones. "That inflammation has a potential or potentially can modulate estrogen response, which could be the link between certain women having heavy periods after the vaccine,” says Dr. Jain.

But not all hope on the data front is lost — people with periods can track their own data in mobile applications, such as Flo, following their vaccine. "We could look at what is the baseline rate of people having irregular cycles, or cycles that are different, and look at whether we're noticing changes in the population of women who've gotten the vaccine in the last few months,” says Dr. Huddleston. 

if my period is irregular following the vaccine, does that mean I could be infertile?

The Centers for Disease Control and Preventation (CDC) has stated that no link has been found between the COVID-19 vaccine and infertility or miscarriages, and it is still highly encouraged by health care professionals that people with periods get vaccinated. If excessive or extremely heavy bleeding begins following the vaccine, seek emergency medical help. 

What’s your experience with the COVID-19 vaccine and your period? Have you noticed irregularities following your vaccination?

Michelle Alexander (she/her) is a freelance writer based out of colorful San Francisco. She enjoys sunny days, oat milk lattes, and hanging out in Mission Dolores Park with her fluffy canine companion, Winston.

by Michelle Alexander