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

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

Their cycles had lengthened, some said. Her bleeding was more profuse.

Research has backed up those anecdotal reports, showing that vaccination against COVID-19 has a temporary but noticeable impact on women’s periods and the symptoms that accompany them.

This is what we know.

Getting vaccinated seems 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 receiving the vaccine.

A study of nearly 4,000 women in the US found that the length of the menstrual cycle was prolonged by approximately 0.7 days after the first dose and 0.9 days after the second dose. Although the cycles were longer overall, the researchers found no change in the number of days the women’s periods lasted.

an even bigger study of nearly 20,000 women in the UK found a similar effect on overall cycle length, but also noted that it lasted longer in people who received both doses of a vaccine within the same menstrual cycle. For these individuals, their cycle length increased by an average of 3.7 days.

An article published on January 7 in the Journal of Infections and Chemotherapy reinforced that finding with new data. The authors calculated the difference between the expected and actual duration of the menstrual cycle in women in Japan before and after vaccination against COVID-19. Before the women were vaccinated, the average difference was about 1.9 days. After two doses of a vaccine, it could be up to 2.5 days. The change was most pronounced in people who received two doses of vaccines within the same cycle, with that group seeing an average difference of 3.9 days.

The changes may not affect everyone evenly beyond the disparities seen with more or less doses. Some people may be more likely to experience interruptions in their cycles than others. One study using long-term data of the US-Canada based Nurses Health Study found that these increases in cycle length were more likely to occur in women whose periods were short, long, or irregular before vaccination.

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

Vaccinated women may also see other period-related symptoms more often.

Another recent study indicates that women are more likely to experience a variety of symptoms that accompany their periods after getting vaccinated.

The study, published December 28 in the journal Influenza and other respiratory virusesanalyzed data from nearly 5,000 women in six Arab countries and found that vaccinated people had back pain, nausea, tiredness, pelvic pain, use of nonprescription pain relievers, and passing loose stools in connection with menstruation more frequently than women unvaccinated people.

Vaccinated people also reported heavier discharge and more days of bleeding, according to the newspaper.

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

The potential effect of COVID-19 infections is less clear

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

Other studies However, with small sample sizes, they have reported that a low percentage of people may experience cycle changes after infection.

What does this all mean?

Research suggests that changes in the length of the menstrual cycle may be occurring due to how the immune system might affect sex hormones. Inflammatory responses to the COVID-19 vaccine can also affect the ovaries and uterus.

However, beyond the apparent impact on menstrual cycles and symptoms, it is not yet known whether COVID-19 vaccines affect fertility and reproductive health. initial studies suggest that vaccination against COVID-19 may not affect fertility.

More studies with larger sample sizes and longitudinal data sets, where researchers follow people and link their data over time, such as with the Nurses’ Health Study, would help improve understanding of how Vaccines affect the bodies and reproductive health of men and women.

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

For example, pregnant people who are not vaccinated may be at higher risk of poor outcomes, as noted by medical experts in a review article published Jan. 12 in the journal. Archives of Gynecology and Obstetrics. The experts detailed that these people were found to have higher rates of hospitalization, intensive care admissions and morbidity rates than their vaccinated counterparts.