Vaccinating against covid-19 after ovulation would prevent possible menstrual disorders

In the midst of a pandemic, social networks highlight new issues of covid-19 such as Vaccine effects on menstruation. Thus, science has shown that immunization against SARS-CoV-2 can generate changes in the duration or bleeding pattern of the menstrual cycle.

Now, the analysis of more than 1,800 cycles from 371 users collected by a mobile app allowed experts from the Artificial Intelligence Research Institute (IIIA-CSIC) to lead a studying which shows how vaccination during the luteal phase, that is, after ovulation, can prevent an increase in menstrual cycle length.

Suspicion first, facts later

It all started from user comments on social media, where they highlighted changes in the menstrual cycle after being vaccinated against covid-19. Given the lack of data, the Lunar App for menstrual cycle monitoring has incorporated a new functionality to voluntarily record the dose, brand and country where the vaccine was received.

Among its users, 371 anonymous profiles were chosen who recorded at least five consecutive menstrual cycles and who were in their third cycle at the time of vaccination. In total, 1,855 cycles were recorded between September 2020 and February 2022.

To analyze the data, this study published in the journal American Journal of Obstetrics and Gynecology It was based on the epidemiological method known as Series of self-controlled cases, in which it is the subject himself who compares the cycles before and after the moment of vaccination.

The importance of the menstrual phase

The variables indicated were cycle length and period of menstruation and variations in bleeding and pain intensity. Finally, the results were screened according to the menstrual phase in which the users were vaccinated.

“It was observed that people who did it during the follicular phase, i.e. before ovulation, had an average increase in cycle length of one day, while people who were vaccinated in the luteal phase did not show an increase”, highlights Velasco.

People who were vaccinated before ovulation had an average increase in one-day cycle length, while people who were vaccinated later had no change.

Borja Velasco, IIIA – CSIC

Among users vaccinated in the follicular phase, 11% increase in menstrual cycle length of more than 8 days, a clinically significant value. Given these data, the study highlights the importance of the menstrual phase for minimize cycle disturbancesand concludes that vaccination during the luteal phase would prevent the potential increase in menstrual cycle length.

These results, observed in the different types and brands of vaccines, are part of “an important and new theme, on which there is still little evidence. Without the awakening of so many people who menstruate and who reported these changes, studies like this would not be carried out”, explains the researcher, who would like the analysis to be replicated with more data and with other methodologies to confirm the findings.