Will the COVID-19 vaccine affect my menstrual cycle?

The outbreak of the 2019 coronavirus disease (COVID-19) pandemic has affected hundreds of millions of people around the world, with a growing wave of illness and death over a two-year period. Even after the severity of the epidemic subsides, concerns remain about the possible long-term consequences of infection and COVID-19 vaccination.

A new paper was published in vaccination The journal reports on the association between COVID-19 vaccination and irregular menstrual cycles.

study: Novel Coronavirus Vaccination and Menstrual Cycle Characteristics: A Prospective Cohort Study. Image credit: GroundPicture/Shutterstock.com

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Thousands of social media posts and Vaccine Safety Surveillance System reports describe menstrual cycle disruptions following COVID-19 vaccination. Postmenopausal women report longer, heavier, and more irregular periods, and in some cases breakthrough bleeding.

For this reason, many have expressed concern that these vaccines may harm women’s reproductive health.

Biologically, the pathway by which vaccine-induced immune responses short-term affect endocrine master glands, the hypothalamus, and the associated pituitary-ovarian axis is highly plausible. This could explain how vaccination theoretically affects the menstrual cycle.

Previous studies have reported acute and transient effects on menstruation for typhoid, hepatitis B, and human papillomavirus (HPV) vaccines.

The current study focuses on six main characteristics of the menstrual cycle: length, regularity, bleeding duration, bleeding intensity, and menstrual cramps, in relation to the menstrual cycle.

Previous studies introduced reporting bias, lacked a control group, did not adjust for confounding factors, failed to assess menstrual characteristics other than cycle length, or lacked sufficient follow-up. was

The researchers used data from Pregnancy Research Online (PRESTO) in this study. This is a group of couples who participated in a survey online.

They were followed before conception and none were undergoing fertility treatment. The study period was from January 2021 to August 2022, and the cohort included couples from the United States or Canada.

About 1,100 couples between the ages of 21 and 45 participated in the study. The questionnaire was assessed at baseline and every 8 weeks thereafter for up to 12 months. Questions were asked about vaccination against COVID-19 and the characteristics of the menstrual cycle.

What did the study show?

Of more than 1,000 participants, approximately 14% sent six follow-up questionnaires, and 65% became pregnant within the next year. Just over 1 in 10 started fertility treatment, and 2% stopped trying to conceive. The remaining 9% discontinued follow-up.

None of the participants had been vaccinated against COVID-19 initially, but almost 40% received one or more vaccinations during the study period. Most of them received Moderna or Pfizer vaccines, 32% and 61%, respectively.

Of the vaccinated group, 7 of 8 were vaccinated between February and May 2021. The majority were more educated, had higher incomes, and were about to have their first baby than the unvaccinated group.

The researchers estimated differences in menstrual characteristics associated with COVID-19 vaccination after adjusting for sociodemographic, reproductive and lifestyle factors, and medical conditions.

After adjustment, the first dose of COVID-19 vaccine was associated with an average extension of 1 day in the next cycle. The corresponding increase in the first cycle after the second dose was 1.3 days. Interestingly, this association was stronger from April 2021 to August 2022 than it was from January 2021 to March.

By the second post-vaccination cycle, these associations weakened, indicating that the effects were transient. Thus, long cycles were more prevalent from about 6% to 11% after the first dose, but the prevalence decreased to 7.3% in subsequent cycles.

There was no strong association between vaccination and menstrual cycle regularity, bleeding intensity, bleeding duration, or dysmenorrhoea.

There was no significant change in the proportion of participants with post-vaccination irregular cycles (15%) after the first or second dose, regardless of vaccine brand. There was no change after adjusting for history of COVID-19 or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Remember, these are not contraceptives, but couples who are trying to conceive, and many are successful. Therefore, follow-up beyond several months was not possible after each vaccination.

Also, older women were deliberately not included in the study. Third, most of the participants were white college graduates.

What is the impact?

In the current study, other than a short one-day delay in the first cycle after each vaccination and a similarly short-lived increase in the prevalence of long cycles, there was no significant difference between COVID-19 vaccination and menstrual function. no relationship was shown. Both of these changes disappeared by the second post-vaccination cycle.

This transient effect is probably due to activation of the immune system mediated by cytokines that interfere with the hypothalamic-pituitary-ovary (HPO) axis.

No association with fertility was observed, and no other menstrual cycle characteristics were shown to change in association with COVID-19 vaccination.

Taken together, these results indicate that short-term changes in menstrual cycle characteristics are unlikely to translate into significant differences in fertility.. “