The COVID vaccine may delay your period by a day or two

key takeaways

  • One study found that participants experienced small, temporary changes in the length of their menstrual cycles after being vaccinated against COVID-19.
  • When one shot was given, the average cycle lengths differed by less than a day. People who get two doses of the vaccine may experience a two-day change.
  • The study’s researchers hypothesized that these changes were related to a biological link between the immune and reproductive systems.

Anecdotal aside, the link between the COVID-19 vaccine and menstrual cycle length has been a mystery until recently. Now, researchers have conducted a study that found that a COVID-19 vaccine may delay menstruation by a day or two.

Researchers analyzed menstrual cycle data from 1,556 unvaccinated and 2,403 vaccinated participants, including:

  • 55% received the Pfizer-BioNTech vaccine
  • 35% received Moderna
  • 7% received Johnson & Johnson

They found that participants’ menstrual cycle length increased by 0.71 days after a single dose of COVID-19 compared to their pre-vaccination cycle. Participants who received two doses of the COVID-19 vaccine in the same cycle experienced a change of about two days.

“The average change in length during an injection cycle is less than one day,” Alison Edelman, MD, MPH, professor of obstetrics and gynecology at the Oregon Health and Science University School of Medicine, told VigorTip. People who get two doses of the vaccine in one menstrual cycle may have a two-day difference.”

The January study was published in the journal Obstetrics and Gynecology.

Can you get the COVID-19 vaccine during your period?

What’s causing the delay?

Although more research is needed to understand the causal relationship between the COVID-19 vaccine and menstrual cycle length, Edelman hypothesized that menstrual changes following COVID-19 vaccination may be related to a biological link between the immune and reproductive systems. Vaccine-related menstrual disorders may be related to the body’s immune response to the vaccine.

“We know that currently available COVID vaccines are effective at activating the immune system,” Edelman said. “The immune system temporarily increases small proteins called cytokines, which may transiently affect a person’s ability to regulate their menstrual cycle, potentially leading to temporary changes in cycle timing.”

Study: Women have more pronounced COVID-19 vaccine side effects than men

More research is needed to decipher the relationship between injections and the menstrual cycle, as well as the possible effects of booster injections.

What should you do if your period is delayed?

Cindy MP Duke, MD, PhD, FACOG, Board Certified OB-GYN, recommends taking note of any period delays and using a period tracking app or diary to track your flow.

“In addition to vaccinations, it’s not uncommon for your period to vary in length by a day or two during each monthly cycle,” Duke told VigorTip.

So a change of less than one day on average suggests there’s no reason to worry and no need for medical attention, Edelman said.

How hormones control your menstrual cycle

“However, if a person’s entire cycle (bleeding from day one to day two) changes over eight days, or if there are significant changes over three months or more, it may be necessary to consult their healthcare provider Yes,” Edelman explained.

what does this mean to you

A change in the length of your menstrual cycle of less than a day shows no reason to worry, experts say. However, if your menstrual cycle length changes by more than 8 days, or has changed significantly within three months, consult your healthcare provider.

reassuring research

Edelman hopes the study will provide answers and validation for individuals whose periods have been interrupted after vaccination.

“As a clinician, I can help them provide information about what to expect about vaccinations, which may include a slight change in their cycle length, and prepare them for that possibility so they don’t have to worry about it,” she said. Say.

Overall, the vaccines were safe, were effective in reducing hospitalizations and deaths, and were not shown to affect fertility in men and women.

“If menstrual disruption is the only reason an individual is not considering a COVID-19 vaccine, then this study should reassure that the underlying changes are minimal and appear to be temporary — and consistent with other research on fertility and pregnancy — — does not appear to cause long-term health or reproductive effects,” Edelman said.

The information in this article is current as of the date listed, which means that you may have updated information as you read this article. For the latest updates on COVID-19, visit our Coronavirus news page.