Do COVID vaccines affect menstruation?

Since the rollout of the COVID-19 jabs, there have been many reports of potential side effects. While most have been ruled out through various studies, one of the most persistent claims has prompted much debate online and in the home. 

Many women have observed irregularities in their menstruation cycles after getting vaccinated against COVID-19. The changes observed range from earlier or later periods that are heavier or lighter, to longer or more painful periods. Some have even said they skipped an entire cycle. 

The effect of COVID-19 vaccines on menstrual cycles, like many other vaccine candidates, was not included as a possible side effect for participants during the 2020 clinical trials. Menstrual side effects are not actively tracked in VAERS , the US-based database that allows vaccine recipients to enter possible side effects themselves. By May 2021, only a small number of individuals (fewer than 200) had self-reported a menstruation-related issue.

New study shows menstrual side effects of COVID jabs

A study published in the journal "Obstetrics & Gynecology" now confirms one phenomenon that some women had observed after getting their coronavirus vaccinations: a change in the length of menstrual bleeding.

According to the study, which collected data from nearly 4,000 users of a smartphone app that tracks menstrual cycles, vaccination against COVID-19 was linked with a small and temporary change in menstrual cycle length. The main finding is that menstruation starts about a day later after the vaccination than in women from an unvaccinated control group.

The timing of the next period changed by less than one day, on average, during the menstrual cycle when the shot was administered. If women received two vaccine doses within a single menstrual cycle, a two-day change was observed, on average. The change was categorized as minimal and, most importantly, only temporary. According to the study, the COVID-19 vaccinations assessed do not have any further effects on the period.

Limited data on effects of COVID vaccines

The study monitored the six consecutive cycles after getting a jab. However, the study only looked at the vaccines produced by BioNTech-Pfizer, Moderna, and Johnson & Johnson. Women who received the AstraZeneca vaccine were not included in the study. More than half of the vaccinated received the BioNTech-Pfizer vaccine (55%); 35% received Moderna, and 7% the J&J/Janssen.

So not all COVID-19 vaccines available in different countries have been considered. One other factor to keep in mind: This study only looked at one of the points raised. According to the study itself, questions remain about other possible changes in menstrual cycles, such as menstrual symptoms, unscheduled bleeding, and changes in the quantity of menstrual bleeding.

Different studies show different outcomes

In December 2021, the European Medicines Agency (EMA) said it had not established a link between changes in menstrual cycles and COVID-19 vaccines, even after a study by the Norwegian Institute of Public Health (FHI) suggested some women had heavier periods after being inoculated.

The Norwegian study had surveyed almost 6,000 women aged 18-30 about their menstrual cycles and bleeding patterns before and after vaccination. There was a generally high incidence of various menstrual disturbances: After the first dose, 39.4% reported at least one change, and after the second dose, 40.9%.

Among the participants, 98.4 % were vaccinated with the first dose, and 91.8 % with two doses. Among these, 59.4 % received BioNTech-Pfizer as the first dose, 35.8 % received Moderna, 4.7 % got AstraZeneca and 0.2 % got Johnson & Johnson.

For dose two, 47.4 % received BioNTech-Pfizer, and 52.6%received Moderna — so only mRNA vaccines. Menstrual changes were reported after both mRNA vaccines, to the same degree.

After reviewing the available evidence, the European Medicines Agency's (EMA)'s Pharmacovigilance Risk Assessment Committee (PRAC) said it had decided to request an evaluation of all available data. 

Menstrual changes are common

According to the EMA, menstrual disorders can occur due to a range of underlying medical conditions, infections, medicines, hormones, contraception, as well as disorders of the uterus and cervix like endometriosis.

Stress and tiredness are other common causes for menstrual changes among people of childbearing age and can have various triggers, according to both studies.

"Maybe a short change in your cycle or a slightly different bleeding pattern is actually related to the immune response that your body produces to the vaccine, which is exactly what we see when you get sick," explains Dr. Jennifer Lincoln, a US-based Gynaecologist, trying to combat misinformation about sexual health on TikTok, Instagram and YouTube in an interview with DW.

But concerns about a possible association between COVID-19 vaccines and irregular menstrual cycles could lead to vaccine hesitancy.

Mis- and lack of information may lead to vaccine hesitancy

The US Centers for Disease Control and Prevention said there is no evidence that the vaccines cause fertility problems.

In addition, a recent report using the v-safe after vaccination health tracker, a monitoring system designed by the CDC to track COVID vaccine side effects, showed that 4,800 people had a positive pregnancy test after receiving the first dose of an mRNA COVID-19 vaccine (produced by BioNTech-Pfizer or Moderna).

Another report using data from eight US healthcare systems documented more than 1,000 people who completed their COVID-19 vaccination (including mRNA and other COVID vaccines) before becoming pregnant.