COVID vaccination could affect menstrual cycle in women

Credit: CDC.

In a study from Oregon Health & Science University, scientists found some people may experience a slight, temporary change in the length of their monthly menstrual cycle following COVID-19 vaccination.

The study builds on prior work from the same research team that first identified an association between COVID-19 vaccines and menstrual cycle changes.

A range of menstrual cycle changes after COVID-19 vaccination have been reported, including longer and shorter cycles, missed cycles, heavier and lighter menstrual flow, and intermenstrual spotting.

However, clinical trials of vaccines do not collect outcomes related to menstrual cycles, leaving a significant gap in knowledge around these issues, prompting Edelman and the team to look more closely at what was being reported by the public.

In the current study, the team used data from more than a quarter of a million menstrual cycles recorded by almost 20,000 individuals using the menstrual cycle tracking application Natural Cycles.

The findings were consistent with results found in the U.S. cohort: Individuals who received two doses of a COVID-19 vaccine in a single menstrual cycle saw an average increase in cycle length of 3.7 days compared with the unvaccinated group.

On average, vaccinated people experienced an increase of less than one day in each cycle in which they were vaccinated: a 0.71-day increase after the first dose and a 0.56-day increase after the second dose.

Vaccinated or not, individuals experienced changes in their cycle length, but a larger proportion of vaccinated individuals had an increase in cycle length of more than eight days (13.5%), compared with those who were unvaccinated (5%).

Additionally, changes in cycle length appeared to be similar across the different vaccine types, offering reassurance to those with concerns about newer vaccine technology.

The team says changes to routine bodily functions can be alarming, and cause fear and anxiety.

They want to emphasize that the menstrual cycle changes at a population level are small and typically resolve in the cycle after vaccination.

Hopefully, this knowledge provides clarity about what people can expect after getting vaccinated.

Individuals who notice prolonged changes in menstruation are encouraged to seek guidance from their clinician.

If you care about COVID, please read studies about a universal antibody therapy to fight all COVID-19 variants, and Vitamin D levels could predict the severity of COVID-19.

For more information about COVID, please see recent studies about people who are 5 times more likely to get COVID-19, and this face mask can capture and deactivate the COVID-19 virus.

The study was conducted by Alison Edelman et al and published in BMJ Medicine.

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