Yes, the COVID19 Vaccine can Change your Period–but only briefly

A new study published in Obstetrics & Gynecology supports what most women have been reporting since vaccination against COVID-19 started: their menstrual cycles or period length change after vaccination. Women have reported their periods were late, their bleeding was heavier than usual or even painful. Even some postmenopausal women have reported having a period after getting vaccinated.


The study tracked data using the “Natural Cycles” app. The sample included 2,403 vaccinated U.S. residents from 18 to 45 years of age who had normal cycle lengths (24-38 days) for three consecutive cycles before getting the first vaccine dose and three vaccine-dose cycles (cycles 4-6). In this group, 55% received the Pfizer-BioNTech vaccine, 35% received the Moderna vaccine and 7% the Johnson & Johnson/Janssen vaccine. The sample also included six cycles of 1,556 unvaccinated women over a similar period of time. The study analyzed each individual’s change in cycle and period length in both groups. 


The results showed that the COVID-19 vaccine was associated with a less than 1-day change in cycle length for vaccine-dose cycles compared to the prevaccine cycles. This delay increased to a 2-day one in women who had both vaccine doses within the same menstrual cycle. The unvaccinated group saw no significant change in their periods. Results also show that changes in period length were not associated with vaccination. For postmenopausal women, on the other hand, bleeding after vaccination could highlight an underlying medical condition.


It is important to note that this study was limited because the sample was not broadly representative as the participants do not use hormonal contraception and weigh less than the average American woman. Still, the small changes in menstrual cycles and length due to vaccination in this study, though real, are small enough not to be harmful. In addition, there are several other studies that support the efficacy and benefits of the COVID-19 vaccine (available in previous entries of this blog), so we still encourage our patients to get vaccinated. 


El Camino Women’s Medical Group offers the latest Minimally Invasive Solutions for gynecologic problems.   Drs. Amy TengErika Balassiano, Pooja Gupta, and Christina Lam, all members of AAGL (American Association of Gynecologic Laparoscopy) are highly trained and experienced in the field of Minimally Invasive Gynecologic Surgery.   Dr. Erika Balassiano has also completed a Minimally Invasive Gynecologic Surgery Fellowship, under the supervision of world-renowned Dr. Camran Nezhat.

All of our physicians are El Camino Hospital doctors and operate and deliver at the Mountain View campus.

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