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Effects of Covid-19 vaccines on menstrual cycle

Date: 10 January 2022 Tags: Miscellaneous


A new study has tried to identify the effects of Covid-19 vaccines on women’s menstrual cycle.



There have not been enough studies carried out on women’s menstrual cycle under the influence of vaccines.



  • The study focused on the data of nearly 4,000 US based individuals. It was published in the journal Obstetrics & Gynecology.

  • Temporary changes in the length of their monthly menstrual cycles can be observed by some people after taking Covid-19 vaccine.

  • Typically, the women who receive Covid-19 may observe that their menstrual cycles start a day later than they are supposed to.


The study

  • The study was conducted using an application called ‘Natural Cycles’. The participants were between the ages of 18 and 45 years and had normal menstrual cycles for three consecutive cycles before taking vaccine.

  • Majority of vaccinated women received the Pfizer-BioNTech vaccine (55 percent) and about 35 percent received the Moderna vaccine.

  • In most cases, the change has been a single day. However, individuals receiving two vaccine doses within the same menstrual cycle may see that their cycle length increase by two days.

  • Such changes vanish quickly and by next cycle normality is restored. However, the vaccines did not impact the length of periods or on bleeding.


Limitations of study

  • The study is not universal as all participants are US citizens, educated, white and do not use any hormonal contraception.

  • There is no enough data to study long term effects on cycle duration after finding that cycles return to normalcy after one cycle.

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