A large international study confirmed the results of a previous US study that linked vaccination against the Corona virus and an increase in the average length of the menstrual cycle by less than one day. The increase was not associated with any change in the number of menstrual days (bleeding days). Funded by the National Institutes of Health, the new study included data from nearly 20,000 people from Canada, the United Kingdom, the United States, Europe and other parts of the world who had received any of nine different vaccines. For most study participants, the increase resolved in the post-vaccination cycle.
The study’s principal investigator was Alison Edelman, MD, MSc in public health, from Oregon Health & Science University in Portland. Appears in BMJ Medicine.
“These findings provide additional information to advise women about what to expect after vaccination,” said Diana Bianchi, MD, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) at the National Institutes of Health. “Changes after vaccination appear small, within the normal range of diversity, and temporary.”
The study was funded by the NICHD and the National Institutes of Health’s Office of Women’s Health Research, which was part of the $1.67 million awarded to five institutions to explore potential links between the COVID-19 vaccine and menstrual cycle changes.
A change in cycle duration of less than eight days is considered to be within the normal range of variation. Although subtle changes in the menstrual cycle may not be meaningful to health care professionals and researchers, the study authors wrote, the observed changes in bodily function associated with fertility could be worrisome for those who experience them and could contribute to vaccine hesitancy.
The researchers analyzed de-identified data from a fertility tracking app, Natural Cycles. Users of the app provided information about their temperature and menstrual cycles. They also had the option to consent to the use of their de-identified data for research purposes. The global spread of COVID-19 vaccines allowed the study authors to expand on their original study of people in the United States. The study included data from participants from all over the world, but most were from the United Kingdom (32%), the United States and Canada (29%) and Europe (34%). In addition to the COVID-19 messenger RNA vaccines (Pfizer-BioNTech and Moderna), participants received COVID-19 vaccines made with engineered viruses (AstraZeneca, Covishield, Janssen/Johnson & Johnson and Sputnik), and inactivated viruses (Covaxin, Sinopharm, and Sinovac).
A total of 19,622 individuals participated. Of these, 14,936 have been vaccinated and 4,686 have not. The researchers analyzed data for at least three consecutive cycles before vaccination and at least one cycle after. Data from at least four consecutive cycles over a similar time period were analyzed for unvaccinated participants.
On average, the vaccinated subjects experienced an increase of less than one day in each vaccinated cycle: an increase of .71 days after the first dose and 56 days after the second dose. Participants who received both doses in one cycle had an increase in cycle length of 3.91 days. After vaccination, cycle duration increased by only 0.02 days for individuals who received one dose per cycle, and .85 days for individuals who received two doses in one cycle, compared to participants who were not vaccinated. Changes in cycle length did not differ according to the type of vaccine received.
Of the total, 1,342 participants experienced a change in cycle length for eight days or more, including 6.2% of vaccinated individuals and 5.0% of unvaccinated individuals. Younger women whose cycle duration was longer before vaccination were more likely to experience an increase.
The authors called for future studies on other aspects of vaccination-related changes in menstrual cycles, such as unexpected vaginal bleeding, menstrual flow, and pain. They also called for studies to determine the physical reasons for such changes.
About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)
from San Jose News Bulletin https://sjnewsbulletin.com/the-study-confirms-the-association-between-vaccination-against-covid-disease-and-a-temporary-increase-in-the-duration-of-the-menstrual-cycle/
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