What To Know About How The COVID-19 Vaccine Affects Your Period

According to the Centers for Disease Control and Prevention, common reactions reported after getting a two-dose or single-dose COVID-19 vaccine — or a booster shot — generally include fevers, headaches, tiredness, and soreness at the injected area. These side effects are commonly found among all genders; however, many people have also noticed other bodily irregularities that are suspected to be caused by the vaccine. For a lot of vaccinated women, a change in their menstrual cycle is one of the most common claims. 

A survey in the journal Science Advances revealed that 42% of vaccinated respondents with regular periods complained of having heavier-than-normal flows. A number of non-menstruating people, including those who'd entered post-menopause or employed long-term contraceptives, experienced bleeding after getting vaccinated. For Kate Clancy, professor of anthropology at the University of Illinois, her first dose of Moderna's vaccine made her menstruate early and "gushing like I'm in my 20s again," she shared on Twitter.

Because of scant clinical trials investigating the side effects of vaccines in the earlier days, it was hard to decide whether the jabs could alter one's period, or people were just becoming more aware of their menstrual patterns after COVID-19 shots. Besides, periods are subject to fluctuations, with or without vaccinations. With more studies conducted on the potential side effects of vaccination, we now have better insights into the impact of COVID-19 vaccines on our bodies. Here's what recently vaccinated people can expect from their menstrual cycles, according to experts.

According to a 2022 study published in the journal Obstetrics & Gynecology, people who got two doses of COVID-19 vaccines within the same menstrual cycle, the interval between periods, might experience changes in their period length by one or two days. These changes constitute no cause for alarm for one's physical health or fertility in the long run, says professor Alison Edelman, the lead researcher of the study.

Meanwhile, an international study polling nearly 20,000 participants across North America and Europe has confirmed a previously established finding that COVID-19 vaccination can extend a menstrual cycle length for less than one day, a news release by the National Institutes of Health states. Cycle lengths of fewer than eight days, per the news release, are perceived to be within the acceptable spans of change. However, this change would usually last for only one cycle after vaccination and clear up by the following period. While each woman's menstrual cycle is unique, most women have periods every 28 days, the U.K.'s National Health Service points out. Variation in cycle length is commonplace, and the acceptable range for a regular cycle is 21 to 40 days.

Aside from briefly extending your menstrual cycle, COVID-19 vaccines can actually affect your bleeding quantity. For instance, only around 8% of the 5,688 women in Norway between the ages of 8 and 50 surveyed by the Norwegian Institute of Public Health reported having a heavy period prior to receiving the vaccination. The prevalence of unusual bleeding patterns increased to 14% following COVID-19 vaccinations. For 21-year-old California resident Caiityya Pillai, who got her shot in March 2021, her typically light menstruation not only got unusually painful for the subsequent two months, but it lasted twice as long as it normally did (via The Washington Post). "The pain wasn't like a normal pain. It was to the point where I was crying and could not get out of bed," she told the outlet. Her period pain exacerbated after her second dose in July, but Pillai admitted she didn't feel alarmed as she had come across several instances of similar post-vaccination period experiences.

While the shifts are short-lived for some people, others have reported enduring disturbances in their menstrual cycles long after vaccination, including heavier bleeding, more extreme mood swings, and longer periods. Most experts don't recommend people visit a doctor after experiencing first-time menstrual irregularities, as they might only be temporary. If the changes are long-lived or you're trying to get pregnant but your periods are always irregular, it's better to visit an obstetrician-gynecologist to get medical advice.