A large cohort study measured how frequently women reported bleeding after receiving COVID-19 jabs.
Women who don’t menstruate — including postmenopausal women and those on contraceptives — were several times more likely to experience unexpected vaginal bleeding after COVID-19 vaccination than before the vaccines were offered, a study1 finds.
When COVID-19 jabs were rolled out globally, many women reported heavier-than-usual menstrual bleeding soon after vaccination. Study author Kristine Blix, at the Norwegian Institute of Public Health in Oslo, wanted to look at the trend systematically, particularly in women who don’t normally have periods, such as those taking contraceptives or who have been through menopause. The work is published in Science Advances.
The team didn’t investigate the reasons for the unexplained bleeding, but suggested that it could be linked to the SARS-CoV-2 spike protein used in the vaccines. In general, the COVID-19 vaccines have been found to be safe and effective.
Blix and her colleagues used an ongoing population health survey called the Norwegian Mother, Father, and Child Cohort Study. “We had already, from the early pandemic, biweekly questionnaires going out to cohort participants to monitor effects of the pandemic,” Blix says. In the first questionnaire that covered COVID-19 vaccinations, sent in 2021, some women reported in free-text fields that they had experienced heavy menstrual bleeding. “This urged us to ask for bleeding patterns in a structured manner,” she says.
Widespread effect
The team looked at more than 21,000 responses from postmenopausal, perimenopausal and non-menstruating premenopausal women — including some who were on long-term hormonal contraceptives.
The results were surprising, says Blix. They found that 252 postmenopausal women, 1,008 perimenopausal women and 924 premenopausal women reported experiencing unexpected vaginal bleeding.
Of these, roughly half of each group said that the bleeding came in the four weeks after the first or second vaccine dose, or both. Premenopausal and perimenopausal women were most likely to report unexpected bleeding in the month after the vaccine, with their risk being three to five times as high as before the vaccinations existed. The risk for postmenopausal women increased by two- to threefold.
Norway used the mRNA jabs made by Moderna and Pfizer–BioNTech, and other vaccines including the one made by AstraZeneca. In October 2022, the European Medicines Agency updated the side-effect information of mRNA vaccines to include heavy menstrual bleeding.
Unexpected bleeding after menopause is usually considered medically serious, and could be an early sign of conditions including endometrial carcinoma and precancerous lesions. Although the cause of the post-vaccination bleeding isn’t clear, if it’s a known side-effect of the shots, physicians can take this into account when evaluating a patient’s condition. “Postmenopausal bleeding is often very concerning and a possible sign of cancer. Knowing a patient’s vaccination status could put their bleeding incidence into context, ” says Kate Clancy, a biological anthropologist at the University of Illinois Urbana-Champaign.
Clancy’s group has published results2 of their own survey showing changes in menstrual bleeding after COVID-19 vaccination. She says that the results align with her team’s findings and could help to inform patients and clinicians.
“The most important contribution of this and other documentation will be that female bleeding patterns are included as end points, or monitored, in clinical trials of new vaccines — and perhaps even drug trials,” says Blix.
“Hooray for another group looking at peri- and postmenopausal people!” says Clancy. “I’m so glad to see more attention on a very underserved group.”
Source: COVID vaccines linked to unexpected vaginal bleeding