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

(The Hill) – Since the start of the pandemic, women have reported experiencing changes in their periods after contracting COVID-19 or being vaccinated against it.

Their cycles had lengthened, according to some. Their bleeding was heavier.

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

Here’s what we know.

Getting vaccinated seems to temporarily lead to longer cycles

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

A study of nearly 4,000 women in the United States found that menstrual cycle length was prolonged by approximately 0.7 days after the first dose and 0.9 days after a 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 larger study involving nearly 20,000 women in the UK found a similar effect on overall cycle length, but also noted that it was prolonged longer in people who received both doses of a vaccine during the same menstrual cycle. For these individuals, their cycle length increased by an average of 3.7 days.

A paper published Jan. 7 in the Journal of Infection and Chemotherapy bolstered this finding with new data. The authors calculated the difference between the expected and actual length 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 can take up to 2.5 days. The change was more pronounced in people who received two doses of the vaccine in the same cycle, with this group seeing an average difference of 3.9 days.

The changes also may not affect everyone equally beyond the disparities seen with more or less doses. Some people may be more susceptible than others to experiencing disruptions in their cycles. A study using long-term data from the US and Canada-based Nurses’ Health Study found that these increases in cycle length were more likely to occur in women with short, long or irregular periods. before vaccination.

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

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

Another recent study indicates that women may be more likely to experience a range of symptoms accompanying their period after being vaccinated.

The study, published Dec. 28 in the journal Influenza and Other Respiratory Viruses, analyzed data from nearly 5,000 women in six Arab countries and found that those vaccinated suffered more frequently from back pain, nausea, fatigue, pelvic pain, use and passing of non-prescribed painkillers. loose stools related to their periods compared to unvaccinated people.

Vaccinated people also reported a higher flow and more days of bleeding, according to the newspaper.

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

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 its cohort.

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

What does all this mean?

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

Beyond the apparent impact on menstrual cycles and symptoms, however, it’s still unclear whether COVID-19 vaccines affect fertility and reproductive health. Early studies suggest that vaccination against COVID-19 may not affect fertility.

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

Overall, the research suggests that the benefits of vaccination may outweigh the reproductive health risks.

For example, pregnant women who aren’t vaccinated may be at higher risk for poor outcomes, as medical experts pointed out in a review article published Jan. 12 in the journal Archives of Gynecology and Obstetrics. Experts said these people had higher rates of hospitalization, intensive care admissions and morbidity rates than their vaccinated counterparts.

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