How does the COVID vaccine affect your period?

January 11, 2022 2 min read

A recent study conducted in the US found that the Covid-19 vaccination may give women a slight delay in the beginning of their period cycle. This delay is only minimal, generally being approximately a day long with scientists confirming that it is nothing to worry about. The length of your period may also be affected. The effects are found to be only temporary.

Period cycles usually last approximately 28 days although the exact number of days varies for each individual. Other factors can also affect the duration or delay of your period cycle including:

  • Stress
  • Weight loss
  • Excess weight
  • Birth control
  • Polycystic ovary syndrome (PCOS)
  • Pregnancy
  • Early perimenopause
  • Thyroid disease


Women who took part in the study were between 18 and 45 years old and not on hormonal contraception. Women who had received the first dose of the vaccine had approximately a 0.64 day increase in their cycle length. Women who had received their second dose saw approximately a 0.79 day increase in their cycle length.

The response of a vaccination on an individual’s immune system can spark the delay. This is because the immune and reproductive system are interlinked. A menstrual cycle is affected by the way your brain communicates with your ovaries and then to your uterus. When your immune system responds to the vaccine, it may affect the communication of your menstrual cycle temporarily.

If you are vaccinated, you may have already experienced this or if you are recently vaccinated you may experience this soon. Scientist are assuring s that the delay is only temporary and nothing to worry about, and is instead just something to recognise and validate for those that may have experienced the delay already.  


Medical Disclaimer: Articles are intended for informational purposes only and should not be used as the basis of patient treatment. Ask a medical professional if you have any health-related questions or concerns.


Additional resources

Aubourg, L. (2022). Don’t freak out if a covid vaccine slightly changes your period cycle, says study.


Shkodzik, K. (2022). How late can a period be before you should worry? 8 reasons for a delayed period.

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