COVID-19 Vaccine May Change, Lengthen Menstrual Cycles

Oct. 6, 2022 – Pamela Jock has always had regular periods, even as she rounded 50 and knew perimenopause was on the horizon. But shortly after receiving the second of a two-series COVID-19 vaccine in June 2020, her cycle began to change. At 52, it could indeed be perimenopause, but Jock had to wonder if the vaccine might have played a role. It turns out, the answer to her speculation is “maybe.” 

A new study, recently published in The BMJ,  did a deep dive into the possible link between the COVID vaccine and irregular periods. The investigation, led by Alison Edelman, MD, a professor of obstetrics and gynecology at Oregon Health & Science University, was prompted by more than 30,000 reports of cycle changes to the United Kingdom’s Medicines and Healthcare Products Regulatory Agency (MHRA). 

Using data from a period-tracking app called Natural Cycles, the study pulled in numbers from more than 20,000 women from around the world. The researchers considered the three menstrual cycles prior to vaccination, and at least one cycle after. They compared this to four menstrual cycles in a group that had not received the vaccine. 

The results revealed that on average, the vaccinated women got their periods 0.71 days late after the first shot. Those who received two vaccines within one cycle saw an increased cycle length of 4 days, on average. This tracks with Jock’s experience. “My cycle elongated to 30 days, versus my normal 26 days,” she says. “Then I had a gap between cycles of a few months.”

This is where the vaccine-cycle link gets murkier. Given Jock’s age, her big gap between cycles could very well be perimenopause, especially since the study only examined women between the ages of 18 and 45, who already had regular cycles. But Jock still wonders. “After I got my first booster in the fall of 2021, my periods flipped back to normal, showing up every 26 days,” she says. “But they were extremely heavy and I was tired and drained.” 

Follow-up bloodwork revealed anemia, potentially as a result. When she asked about a potential vaccine-irregular cycle link, says Jock, “The doctor didn’t think there was a connection, and that it was probably perimenopause.”

What’s Going On 

Whether in the age range of the people in the study or beyond, like Jock, the relationship between the COVID vaccine and menstrual cycle changes can stem from several things, says Esther Goldsmith, an exercise physiologist with bio-analytics company Orreco. 

“It may be influenced by when in your cycle you have your vaccination,” she says. “We know that changes in estrogen and progesterone in the menstrual cycle can affect the immune system and our immune responses. That’s why I think it’s really interesting that the study shows that those who had two doses in the same cycle were most affected.” 

Orreco’s data collection – which often focuses on female athletes – has shown the vaccine can have other impacts, as well, that may play a role. 

“We’ve also seen that the vaccine can affect oxidative stress and inflammation, things we measure through point-of-care blood analysis,” Goldsmith says. “Inflammation can influence symptoms, so using inference, the vaccine may also illicit a change in menstrual cycle symptoms.” 

Shaghayegh DeNoble, MD, with Advanced Gynecology and Laparoscopy of North Jersey, says she hears from many patients that their periods came later than expected, and/or that they were having heavier than normal periods after the vaccine – as well as after a COVID infection. 

“I remind them that many things can change our cycles, including travel, the change of seasons, and stress,” she says. “This happens all the time, and there are no long-term effects. I reassure them their cycles will return to normal.”

The research found that in most cases, normal occurred within one to two cycles after the vaccine, which aligns with what DeNoble’s patients reported, too. 

Putting Minds at Ease 

While the research may have established a probable connection between the vaccine and abnormal menstrual cycles, Goldsmith and DeNoble both emphasize the shots do not impact fertility. 

“I receive so many phone calls from women worrying that because their periods were off, their fertility may be at risk, too,” DeNoble says. “But fertility is not diminished due to the vaccine.” 

Jock says she is thankful fertility is not something that matters to her, anymore. “I would probably be worried if it were,” she admits. 

Goldsmith says such fears are unwarranted and wants women to put any alarm aside. “An abnormal period is a very natural response to something that is physiologically a big event for your body to deal with,” she says. “Menstrual cycles can be incredibly sensitive to change of all sorts, whether nutrition, lifestyle, stress, or the immune system. We shouldn’t be surprised, therefore, that it will respond to things like vaccines. This probably isn’t a new phenomenon, but it may not have been documented in the past.” 

Now armed with the research results, DeNoble says it will be easier to educate patients about what to expect with boosters. 

“It’s so important for us to be able to warn patients about potential side effects,” she says, “and it’s also important that we can put their minds at ease.” 

Goldsmith recommends that women track their cycles, documenting any changes – vaccine or not. 

“We should all pay attention to our cycles and make sure we’re looking after ourselves in these times in order to reduce the stress the body is under,” she says. 

While Jock will never know for certain if her irregular cycles were the result of the vaccine or perimenopause, she’s watching what happens when she soon receives the bivalent COVID vaccine. “I’m curious to see if this carries me along the same trajectory,” she says. 

Regardless of the inconvenience of an abnormal cycle, Jock has no regrets about getting the vaccine, she says: “I’d much rather stay healthy and avoid COVID.”