Soon after the vaccines for Covid-19 were launched in 2021, messages claiming that women should not get the shot during their menstruation went viral. While gynecologists claimed that it was safe, many of them also pointed out that there was no research done on the post-vaccination effects on menstruating women. Afterall, there was no study done on it.
Now months later, a global study of nearly 20,000 people around the world has established that the vaccine for Coronavirus does indeed impact the menstrual cycle.
The data published in the British Medical Journal, taken from a period-tracking app, confirms an average increase in menstrual cycle length of less than one day with the vaccination.
A previous study in the US that is still undergoing peer review suggested that the Coronavirus vaccine may cause heavier periods.
The BMJ study that revealed covid-19 vaccination is linked with an increase in menstrual cycle length was drawn from the data uploaded largely by people in the UK (32%), U.S and Canada (29%) and Europe (34%), and other countries.
How Was The Study Conducted?
Dr. Alison Edelman, professor of obstetrics and gynecology at Oregon Health & Science University, and her team have conducted the largest study ever to understand the impact of Covid vaccination on menstrual cycle.
The researchers analysed data from both vaccinated and unvaccinated people and compared the menstrual cycles before and after the vaccination.
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Last year, Dr. Kate Clancy, an associate professor at University of Illinois, observed that post-vaccination her first period was heavier than usual. Clancy said that a week and half after getting the first dose of the Moderna vaccine, she started her periods and experienced heavy bleeding.
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Clancy's friend shared her experience on her post which prompted her to crowdsource a list asking women whether they noticed any changes. Clancy received many responses from women sharing their experiences of any changes in their periods, the cycles post-vaccination.
"Unfortunately, menstruation has not been considered as a factor while pregnancy and lactating women were considered as factors in the COVID-19 clinical trial factors," Dr. Rishma Pai, consultant gynecologist at Jaslok Hospital had told BOOM.
Researchers analysed de-identified data from the fertility tracking app, Natural Cycles. App-users provided information on their temperature and menstrual cycles. Out of the total 19, 622 individuals who participated, 14,936 were vaccinated and 4,686 were not.
Researchers observed data on at least three consecutive cycles before vaccination and at least one cycle after. Data from at least four consecutive cycles were analysed over a similar time interval for unvaccinated participants.
Here are the most important takeaways from the study:
Increase In Menstrual Cycle Length
The study found that the vaccinated cohort had a less than one-day unadjusted mean increase in the length of their menstrual cycle during the first vaccine dose cycle, compared with their three pre-vaccination cycles.
Specifically, the researchers found a 0.71 day increase after the first vaccine dose and a 0.56-day increase after the second shot.
The unvaccinated cohort, on the other hand, had no significant change in their designated vaccine cycle compared with their first three cycles.
The proportion of individuals who had a change in cycle length of eight days or more was significantly higher in the vaccinated group during both the first and second vaccine dose cycles.
Participants who received both doses in a single cycle had a 3.91-day increase in cycle length. After vaccination, cycle length had increased by only .02 days for individuals who received one dose per cycle, and .85 days for individuals who received two doses in one cycle, compared to participants who were not vaccinated.
Changes in menstrual cycle length did not differ according to the type of Covid vaccine received.
Dr. Edelman said that the immune and reproductive systems are linked and that inflammation or a strong immune response could trigger menstrual fluctuation.
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No Impact On Fertility
Last year as the Covid vaccinations came in, social media was filled with viral rumors. One of them was that vaccination can cause infertility.
In fact, a video post claimed pharmaceutical giant GlaxoSmithKline's COVID-19 vaccine contains ingredients that will cause infertility, and that immunized men can make unvaccinated women sterile, which would cause a global population decline. This is false; the drug company does not have its own COVID-19 vaccine, and doctors say such shots could not cause infertility.
The researcher of the new study that found a connection between Covid shots and menstrual cycle said that there were no indications that the period side effects had any impact on fertility.
Comparisons With Other Studies
The findings of the study in consideration are consistent with a study limited to a U.S.-only cohort. It further proves evidence of small cycle length changes associated with the covid-19 vaccines.
Even after differences in local factors such as vaccine rollout and dosing guidelines between the US and countries included in the latest study, researchers found findings between the two studies consistent.
Researchers have said cycle length changes associated with mRNA (messenger RNA) vaccines do not appear to differ from those with other vaccine mechanisms.
Scope For Additional Research
There's still plenty of research to be done.
This particular study did not look at the heaviness of periods or other side effects such as cramps. The study also only looked at people with normal menstrual cycles who aren't using hormonal contraceptives.
"Now we have information to know that the vaccine does change the menstrual cycle, at least on a population level. It looks like a brief change, and it goes back to normal pretty quickly. But it's important information to have," Dr. Edelman, the researcher said.
The National Institutes of Health has funded at least four other research projects around coronavirus vaccines and menstruation — some of which look at adolescents and people with endometriosis.
A cycle-length increase of less than a day may seem small, but the researcher said that it's important to acknowledge that vaccines can have an effect on periods.
