Researchers Will Examine Link Between COVID-19 Vaccines and Period Changes

As more and more people received their COVID-19 vaccines, reports came to light about short-term changes to periods. Following their shots, some people experienced lighter or heavier bleeding, irregular or missing periods, breakthrough bleeding or spotting, and other menstrual changes.

Now, researchers are beginning to formally examine the connection.

Last month, the National Institutes of Health (NIH) awarded one-year supplemental grants amounting to $1.67 million to study whether COVID-19 vaccines are associated with menstrual changes.

The grant was awarded to five institutions including, Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University, and Oregon Health and Science University.

Experts say many factors can affect menstruation. Researchers will begin conducting studies to assess whether these symptoms can be attributed to vaccination.

How Can Vaccines Potentially Affect Menstruation?

The mechanism behind the vaccine’s potential effects on menstruation is yet to be determined.

“A normal menstrual cycle requires the cooperation of multiple organs in a highly coordinated fashion,” Hugh Taylor, MD, chair of obstetrics, gynecology and reproduction sciences at the Yale School of Medicine and Yale Medicine, tells Verywell. “Not surprisingly, it is easily perturbed, and menstrual irregularity is a very common problem with many causes.” 

For instance, minor factors without long-term health implications can temporarily change menstrual cycles, like mild illness, changes in diet, and even stress. This is why it’s not surprising that stress about the pandemic or flu-like side effects from the vaccine, can potentially alter menstruation as well, he adds.

"We don't yet know if there's definitely a link here, or if menstrual changes that would have happened anyway are being attributed to the vaccine,” Victoria Male, PhD, lecturer in reproductive immunology at the Imperial College London, tells Verywell. “But we can imagine some ways in which vaccines might impact periods.”

Some suspect that there might be a specific component in the vaccine affecting the menstrual cycle. But since irregularities have been reported after both mRNA and adenovirus vector vaccines, this might not be the case.

“For example, we know that the immune response can affect sex hormones, and sex hormones drive the menstrual cycle, so that could be a mechanism,” Male says. “We also know that immune cells in the lining of the uterus help mediate its build up and break down, so if the immune activation associated with vaccination affects those, that could be a mechanism.”

COVID-19 infection was also observed to disrupt the menstrual cycle in about 25% of cases, so it’s possible that the body’s immune response in general—whether to natural infection or vaccination—is causing the menstrual side effects, she adds.

“Unfortunately, menstrual changes are not typically reported in vaccine trials,” Taylor says. “There are some studies that suggest menstrual cycle disturbances with some other vaccines. It is important to study these changes and learn what causes them to assure that they are not serious or long-lasting.” 

Studying the Association Is Crucial

The reported menstrual irregularities were mostly short-lived, but experts say it’s still important to keep studying their potential link to COVID-19 in order to:

• Address unfounded concerns that may cause vaccine hesitancy
• Show that vaccine safety is being taken seriously, even when the potential side effect is not particularly harmful
• Understand the menstrual side effects and allow people to adjust accordingly

Some people are hesitant to take the vaccine in fear that it will affect their fertility in the long run, and their concerns may be addressed by looking into these reports. This will allow scientists to provide further evidence that there is no effect on fertility. Having a richer understanding of the extent of the menstrual side effects also allows people to prepare for potentially altered cycles.

“If the timing of periods is changing, the timing of ovulation might also change,” Male says. “And if that's the case, it's important for those who rely on knowing when they ovulate, either to conceive or to avoid conception, to factor that into their plans.”

Although it’s been nine months since the vaccine rollout began, the potential side effects on menstruation were not evident at first because it was initially offered to people aged 65 and above, aside from long-term care facility residents and healthcare personnel.

“It was difficult to see a link at first because we were vaccinating those who are post-menopausal,” Male says. “Even when we started vaccinating age groups that might be perimenopausal, most people would attribute a change in their period to the kinds of menstrual changes that are common as people come towards the end of their menstruating lives. So it was only when we started vaccinating lots of people in their 30s and 40s, in the spring and summer, that we got a lot of reports of this.”

You Should Get Vaccinated Anyway

Despite the potential menstrual irregularities, it’s still important for everyone to get the vaccine.

“Even if the vaccine does cause menstrual changes in some people—which we still don't know for sure—it's better than getting COVID,” Male says. “COVID causes menstrual irregularities, but worse than that, it can also make you very sick, or you might spread it to someone you love, and they could become very sick.”

There is no evidence showing that COVID-19 vaccines are linked to infertility. The American College of Obstetricians and Gynecologists (ACOG) recommends it for all people who consider getting pregnant in the future. 

“While menstrual irregularity can be alarming and persistent changes deserve medical attention, short-term changes are not a serious concern,” Taylor says. “COVID infection can be a serious and life-threatening condition. The advantages of COVID vaccination cannot be overemphasized. In particular, women who get COVID while pregnant have a much higher risk of serious disease and even death. We highly recommend the COVID vaccine. The benefits clearly outweigh the minor side effects.”

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