What we know about how COVID-19 vaccines affect menstrual cycles

Since the beginning of the pandemic, women have reported experiencing changes in their menstrual cycle after contracting COVID-19 or being vaccinated against it.

Some said their cycles have increased. Their bleeding was more profuse.

Research has backed up those anecdotal reports, demonstrating that the COVID-19 vaccine has a temporary but noticeable effect on women’s periods and associated symptoms.

Here is what we know.

Vaccination appears to temporarily lead to longer cycles

Several recent studies have found that the length of people’s menstrual cycles can increase by up to a day immediately after vaccination.

a A study of nearly 4,000 women In the United States, menstrual cycle lengths were found to be extended by 0.7 days after the first dose and 0.9 days after a second dose. Although the cycles were generally longer, the researchers found no change in the number of days the women’s menstrual cycles lasted.

even bigger A study of nearly 20,000 women In the UK found a similar effect on total cycle length, but also noted that it was extended to a longer duration in people who got two doses of the vaccine in the same menstrual cycle. For these individuals, their cycle length increased by an average of 3.7 days.

Paper published January 7 in Journal of Infection and Chemotherapy This result is reinforced by new data. The authors calculated the difference between expected and actual menstrual cycle lengths in women in Japan before and after COVID-19 vaccination. Before the women were vaccinated, the average difference was about 1.9 days. After two doses of the vaccine, it can be up to 2.5 days. The change was most pronounced in people who received two doses of the vaccine during the same cycle, with that group seeing an average difference of 3.9 days.

The changes may also not affect everyone uniformly beyond variances seen with more or less doses. Some people may be more likely to have disturbances in their cycles than others. One Study using long-term data From the Nurses’ Health Study in the United States and Canada found that these increases in cycle length were more likely to occur in women who had short, long, or irregular periods prior to vaccination.

Studies have found that most people’s menstrual cycles return to normal after one or two cycles.

Women who are vaccinated may also see other symptoms associated with their period more often

Another recent study suggests that women may be more likely to experience a range of symptoms associated with their cycles after vaccination.

The study, published December 28 in the journal Nature Influenza and other respiratory virusesanalyzed data from nearly 5,000 women in six Arab countries and found that vaccinated individuals experienced back pain, nausea, fatigue, pelvic pain, use of nonprescription analgesics, and the passage of loose stools in connection with menstruation compared to unvaccinated individuals.

The paper reported that vaccinated people also reported a heavier flow and bleeding for more days.

The authors note that more data are needed to confirm these findings.

The potential impact of COVID-19 infection is less clear

The study, based on long-term data from the Nurses’ Health Study, indicated that COVID-19 infection did not affect cycle length in the group.

Other studies With small sample sizes, however, I reported that a low percentage of subjects may experience cycle changes after infection.

What does all this mean?

Research indicates that changes in the length of the menstrual cycle may occur due to the immune system’s effect on sex hormones. Inflammatory responses to the COVID-19 vaccine may also affect the ovaries and uterus.

Other than the apparent effect on menstrual cycles and symptoms, it is still uncertain whether COVID-19 vaccines affect fertility and reproductive health. Preliminary studies We suggest the COVID-19 vaccination It may not affect fertility.

More studies with larger sample sizes and longitudinal data sets, where researchers follow up with individuals and correlate their data over time as with the Nurses’ Health Study, should help improve understanding of how vaccines affect men’s and women’s bodies and reproductive health.

Overall, research indicates that the benefits of vaccination can outweigh the risks when it comes to reproductive health.

For example, unvaccinated pregnant women may be at greater risk of poor outcomes, medical experts explain in a review paper published Jan. 12 in the journal Cancer. Archives of Obstetrics and Gynecology. Experts explained that these people were found to have higher rates of hospitalization, critical care admissions, and morbidity rates than their vaccinated counterparts.

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