The Menstrual Cycle and COVID-19 Vaccine

  • 1st Revision: Isobel Lester
  • 2nd Revision: Sophia Bradshaw
  • 3rd Revision: Jasmine Yeh [Linkedin]

As people in UK continue to receive booster shots, a large part of the population across the globe is yet to be vaccinated.1 

This can be attributed to vaccine hesitancy. In particular, a large number of women belong to the section of unvaccinated individuals who are hesitant about getting vaccinated.2 This may be linked to large amounts of misinformation and concerns, brought about especially by the anti-vaccination community, which is primarily dominated by women. Another factor contributing to this may be gender stereotyping in many parts of the world.

Some common side effects experienced after vaccination include headache, fever, chills, nausea, soreness, pain, fatigue, flu-like symptoms such as a cold, runny nose, temperature, and more.3 These side effects are generally mild and may not appear at all in some individuals. 

However, these commonly reported side effects do not cover an important side effect that has been reported by women worldwide post-vaccination from different types of vaccines.

In the U.K., using the MRHA yellow card scheme utilized for reporting the side effects of the vaccine, roughly 30,000 women have reported changes to their menstrual cycle.4 

Menstrual side effects explained

According to these reports, some individuals reported heavy bleeding during their menstrual cycle, while others reported lighter than usual bleeding post-vaccination of both doses. There were also reports of alterations to the menstrual cycle, whereby certain people have reported missed or delayed periods. However, there is no known link between the menstrual cycle and vaccination against COVID-19. Menstrual cycles involve high levels of hormones, and due to the varying levels of hormones in the body, it is often difficult to specifically link the variations in the menstrual cycle to vaccinations in general, let alone the COVID-19 vaccine. 

Possible explanations for changes in the menstrual cycle

One current theory states that menstruation involves certain mechanisms that cause inflammation in the body. The vaccine too causes an inflammatory response, which causes cytokines (proteins imperative in regulating immune cell growth and activity) to trigger an immune response upon receiving the vaccine.6 With regards to studies using animal models, there is suggestive evidence that inflammatory markers may affect the receptors (i.e., cells or parts of tissue responsive to stimuli, in this case hormones) responsible for estrogen expression. Estrogen plays a vital role in menstruation, thereby interlinking the vaccine side effects to menstruation.

Inflammation also plays an important role with regards to the menstrual cycle. It can alter the ways in which the uterine lining degenerates and sheds, potentially causing heavier bleeding.7

Stress is also an important factor to consider whilst understanding the link between the COVID-19 vaccines and changes in the menstrual cycle.8 During a state of stress, the female anatomy temporarily changes to prevent pregnancy in addition to preserving the energy of the body. The vaccine can possibly induce this state in females causing the associated side effect of missed or delayed periods.

The menstrual cycle is an extensive and complex process that is subject to great amounts of change. It is highly dependent on a variety of factors, such as hormone levels, environmental stress, usage of medical and/or herbal supplements, change in medication and/or contraceptive pills, and more. These factors are also worth considering when assessing the relationship between the disruptions in the menstrual cycle of women that have been vaccinated against COVID-19. 

Duration of side effects

It is important to note that all the side effects of the COVID-19 vaccines are short lived. While most symptoms usually disappear in a few days, the changes in the menstrual cycle are temporary as well, yet may last slightly longer, for up to one or two cycles.

Seeking help

In young menstruating individuals, a change or irregularity is quite common, with or without the vaccination. All the side effects of the vaccine, however, should be discussed with your local healthcare provider or reported in accordance with the set guidelines. This can help researchers understand the true extent of the side effects brought about by the vaccine. However, in post-menopausal women, a sign of bleeding post-vaccination is something that has to be discussed with your doctor.

Vaccination and Fertility

Irregularity in the menstrual cycle may be a cause of concern for many women, especially if they are trying to conceive. There are certain myths that revolve around this subject. For example, many individuals believe that the mRNA (genetic material) technology used in a variety of the COVID-19 vaccine is relatively new and does not have substantial evidence to support the claims that it does/does not cause infertility.9 However, this is untrue, as the first vaccine trial using the mRNA technology was conducted in 2006, roughly 15 years ago.

Based on past and current research, there has been no evidence to support the claims that the technology can lead to infertility. The mRNA in the vaccines stays within the body for a short period of time, after which it degenerates and rapidly gets destroyed within the body. Therefore, it has no potential to affect the DNA in the cells of the body. 

There is also a belief that infertility may be caused by the COVID-19 vaccine due to the presence of a protein called syncytin-1, which is found in the placenta.10 Syncytin-1 shares some similar characteristics with the genetic material found in the virus causing COVID-19. As a result of the similarity, some believe that this may cause the body to attack this protein as it mistakes it for being the foreign protein. However, it is important to understand that even though the similarity exists, the genetic makeup and structure of the protein in the virus causing COVID-19 is different from that of the placental protein. 

Additionally, many governing bodies across the world have recommended that women who are pregnant or are planning to get pregnant should receive the vaccine, as it is the best way to prevent infection from the virus to protect themselves and the community during the pandemic.11


To conclude, COVID-19 vaccines are safe, with mild side effects. The disruption in menstruation may be a side effect, but it is temporary, just like all the other side effects. It is extremely important to get vaccinated. Multitudes of trials have been conducted to prove their efficacy and safety, in addition to the fact that the reported cases of individuals affected by COVID-19 have reduced. It is important to get both doses of the vaccine, as well as the booster, in order to protect ourselves and reduce the adverse effects in the event of contracting the virus. 


  1. US approves Covid booster jabs for some older and at-risk Americans. BBC News [Internet]. 2021 Sep 23; Available from:
  2. “There is a lot of distrust”: why women in their 30s are hesitant about the Covid vaccine. The Guardian [Internet]. 2021 Feb 2; Available from:
  3. CDC. Possible Side Effects After Getting a COVID-19 Vaccine [Internet]. Centers for Disease Control and Prevention. 2021. Available from:
  4. Nast C. Two studies have confirmed a link between the Covid-19 vaccine and periods [Internet]. Glamour UK. 2021 [cited 2022 Apr 30]. Available from:
  5. McLean wins NIH grant to explore links between COVID-19 vaccine and menstrual cycle changes [Internet]. 2021. Available from:
  6. Zhang J-M, An J. Cytokines, Inflammation, and Pain. International Anesthesiology Clinics. 2007;45(2):27–37.
  7. Expert reaction to an opinion piece about menstrual changes after covid-19 vaccination | Science Media Centre [Internet]. [cited 2022 Apr 30]. Available from:
  8. Stopped or missed periods [Internet]. 2017. Available from: 
  9. Sep 23, information 2021 | F more, Blackadar contact K. Busting myths about COVID-19 vaccines and fertility [Internet]. UBC News. 2021 [cited 2022 Apr 30]. Available from:
  10. Does the COVID-19 Vaccine Affect Fertility? Here’s What the Experts Say [Internet]. Available from:
  11. Pregnancy, breastfeeding, fertility and coronavirus (COVID-19) vaccination [Internet]. 2021. Available from:
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Ishana Gole

Master of Science - MS, Bioscience Entrepreneurship, UCL (University College London)
Ishana is a Biomedical Science student with a keen interest in neuroscience and past experience in online consulting, marketing and advertising.

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