Vaccination may prolong menstrual cycle

22:59   11 January, 2022

Coronavirus vaccination may cause changes in the menstrual cycle, but it is likely safe and temporary, Oregon Health and Science University scientists said.

According to, the scientists analyzed data from 4,000 women who use the Natural Cycles fertility tracking app. Of these, 2,400 received both doses of one of the mRNA vaccines (Pfizer or Moderna), and another 1,500 participants were not vaccinated. Researchers obtained data on 3 consecutive cycles before vaccination and another 3 after vaccination and compared them with information on 6 menstrual cycles in unvaccinated women.

The vaccinated women were found to have an increased menstrual interval by an average of one day after the first component of the vaccine. At the same time, the duration of menstruation itself did not change. According to scientists, these fluctuations are within the normal range and are not pathological. Moreover, the increase in the menstrual cycle was temporary in most of the participants.

According to the scientists, this study was one of the first of its kind, since the effects of various vaccines (not only for coronavirus) on the menstrual cycle had not been studied before.

In the near future, scientists want to assess the relationship of vaccines to other menstrual characteristics: bleeding intensity, mood changes, weight changes, and pain sensations.

© Medicine