Period disruption due to Covid-19 vaccine

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Dear Dr. Emma,

My cycle seems to be disrupted and I think it’s because of the Pfizer vaccine. Why did this happen? When is it going to come back in balance? And how can I help my body/health/hormones?

Kind regards

Dear Gripie,

Thank you for reaching out! I'm sorry you have experienced changes to your period since your vaccine but don't worry - this happens and it's common. While the most widely reported side effects of Covid-19 vaccines include a sore arm, fever, fatigue and muscle aches, there are still over 30,000 reports (and counting!) (1) of changes to periods and unexpected vaginal bleeding, with the majority of cases reported in primary care and reproductive health centers.

In order to answer your question and to debunk common misconceptions about Covid-19, vaccines and their effect on menstrual cycles and periods, let’s explore 5 of the biggest myths out there.

Myth 1: Menstrual changes are possible after Covid-19 vaccinations.


According to Dr Jackie Maybin, Senior Clinical Research Fellow and Consultant Gynaecologist at the University of Edinburgh’s MRC Centre for Reproductive Health, the most reported disturbances are changes in the duration, regularity, frequency and the volume of menstrual flow (2).

Myth 2: Menstrual changes are more likely with a specific type of vaccine.


Covid-19 vaccines help our bodies develop immunity to the virus that causes Covid-19 without us having to get the illness (3). While scientists don't yet understand exactly how vaccines could cause period changes, menstrual changes have been reported after both mRNA (Pfizer/BioNTech, Moderna) and adenovirus vectored (Oxford Universit/AstraZeneca, Janssen) vaccines (4).

This suggests that, if there is a connection, it is likely to be a result of the immune response to vaccination rather than a specific vaccine component. But let’s dive into this further, with what we do know about reproductive hormones and the immune system:

Normally, the brain, ovaries and womb interact to control the menstrual cycle. So menstrual disturbances can either happen when:

  • There is a trigger affecting the part of the brain that controls reproductive hormones.

Stress, stress, stress. We cannot stress (pun intended) the impact of this on our hormone levels, enough! Life stressors, pandemic life and even anxiety surrounding getting vaccinated, can all tamper with the signals our brain sends to the ovaries and the womb, causing physiological changes that impact our menstrual cycles.

  • There is a trigger affecting the ovaries

Besides being affected by the altered brain signals stress may induce, the ovaries can also be directly influenced. Covid-19 vaccinations are designed to stimulate an immune response in the body to protect it against future Covid-19 infection. The inflammation resulting from this may temporarily affect the ovaries, affecting their hormone production over one or two cycles and resulting in irregular or heavier menstrual bleeding. Actually, one study found that a quarter of women who had Covid-19 virus, also experienced changes to their menstrual cycle (5). So a link between infection, immune responses and reproductive changes has been demonstrated.

  • There is a trigger directly affecting the lining of the womb (which is what is shed during a period).

Our womb lining - aka the endometrium - is made up of immune cells that work as part of our immune system (6). As a result, these cells also become stimulated after the vaccine. This time, inflammation may temporarily alter how the endometrium breaks down and sheds, causing a heavier and/or more painful period. It’s worth knowing that other vaccines, such as HPV or human papillomavirus, have also had similar reported effects on menstruation (7). Certainly, more studies are needed exploring the links between immune responses and reproductive health.

Myth 3: Changes to your menstrual cycle are permanent.


Most people who report a change to their period after vaccination find that these changes generally last only one or two cycles, after which things return to normal. Why, you might ask? Well it’s because immune system responses are rapid but they do subside quickly (8). This is why you might experience the more common side effects after your jab, such as a sore arm or fatigue, for a few days afterwards. And it’s also why any impact on your womb lining immune cells would only be apparent when the lining sheds i.e. your period.

Myth 4: Covid-19 vaccinations increase your chances of infertility.


There is currently no evidence that Covid-19 vaccination adversely affects fertility (9, 10, 11). In fact, clinical trials of Covid-19 vaccines have found unintended pregnancies occurred at similar rates in both vaccinated and unvaccinated groups (12). Fertility measures and pregnancy rates were also found to be similar in both vaccinated and unvaccinated patients in assisted reproduction clinics (13, 14). These results demonstrate that fertility is not impacted by vaccination, but further studies into this are ongoing.

Myth 5: Any changes to your menstrual cycle after getting vaccinated, are probably nothing to worry about.


Although reported changes to the menstrual cycle after vaccination are short lived, it is always important for anyone who experiences heavy or unusual vaginal bleeding, to speak to a healthcare professional for advice regardless of whether you have been vaccinated or not (15). This is especially important after menopause, as post-menopausal bleeding can sometimes be a symptom of underlying serious conditions such as cancer. In a nutshell, seek advice if you are unsure. And even if you experience no changes, remember that good menstrual health stems from a healthy, balanced diet, managing your stress levels and regular exercise.

Myth 6: I can’t take a Grip test if I have been vaccinated against Covid-19.


Although a Grip test can be useful for identifying other causes of an irregular cycle and/or period abnormalities, it is important to prick on day three of your period. For that reason, we recommend waiting a few months after your vaccine to give your cycle time to return to what is normal for you. After this time, you can prick more accurately and therefore get more accurate results.


  1. GOV.UK. 2021. Coronavirus vaccine - weekly summary of Yellow Card reporting. [online] Available at: <>.

  2. Royal College of Obstetricians & Gynaecologists. 2021. RCOG responds to reports that COVID-19 vaccine affects periods. [online] Available at: <>.

  3. Centers for Disease Control and Prevention. 2021. Understanding How COVID-19 Vaccines Work. [online] Available at: <>.

  4. Menstrual changes after covid-19 vaccination. 2021. [online] Available at: <>.

  5. Li, K., Chen, G., Hou, H., Liao, Q., Chen, J., Bai, H., Lee, S., Wang, C., Li, H., Cheng, L. and Ai, J., 2021. Analysis of sex hormones and menstruation in COVID-19 women of child-bearing age. [online] Available at: <>.

  6. Vallvé-Juanico, J., Houshdaran, S. and Giudice, L., 2019. The endometrial immune environment of women with endometriosis. Human Reproduction Update, [online] 25(5), pp.565–592. Available at: <>.

  7. Gong, L., Ji, Hh., Tang, Xw. et al. Human papillomavirus vaccine-associated premature ovarian insufficiency and related adverse events: data mining of Vaccine Adverse Event Reporting System. Sci Rep 10, 10762 (2020).

  8. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. How does the immune system work? [Updated 2020 Apr 23].Available from:

  9. Orta, O., Hatch, E., Regan, A., Perkins, R., Wesselink, A., Willis, S., Mikkelsen, E., Rothman, K. and Wise, L., 2021. A prospective study of influenza vaccination and time to pregnancy. [online] Available at: <> [Accessed 10 October 2021].

  10. Bentov Y, Beharier O, Moav-Zafrir A, et al. Ovarian follicular function is not altered by SARS-Cov-2 infection or BNT162b2 mRNA Covid-19 vaccination. medRxiv 2021:2021.04.09.21255195. [Preprint.] doi:10.1101/2021.04.09.21255195

  11. Safrai M, Rottenstreich A, Herzberg S, Imbar T, Reubinoff B, Ben-Meir A. Stopping the misinformation: BNT162b2 COVID-19 vaccine has no negative effect on women’s fertility. medRxiv 2021:2021.05.30.21258079

  12. Male V. Are covid-19 vaccines safe in pregnancy?Nat Rev Immunol2021;21:200-1. doi:10.1038/s41577-021-00525-y pmid:33658707

  13. Morris RS. SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility. F S Rep2021.doi:10.1016/j.xfre.2021.05.010. Pmid:34095871

  14. Orvieto R, Noach-Hirsh M, Segev-Zahav A, Haas J, Nahum R, Aizer A. Does mRNA SARS-CoV-2 vaccine influence patients’ performance during IVF-ET cycle?Reprod Biol Endocrinol2021;19:69. doi:10.1186/s12958-021-00757-6 pmid:33985514

  15. GOV.UK. 2021. COVID-19 vaccines: updates for August 2021. [online] Available at: <>.