The researchers suggested it could have been connected to the SARS-CoV-2 spike protein in the vaccines. The study was published in Science Advances.
After vaccinations became widely available, many women reported heavier menstrual bleeding than normal. Researchers at the Norwegian Institute of Public Health in Oslo examined the data, particularly among women who do not have periods, such as those who have been through menopause or are taking contraceptives.
The researchers used an ongoing population health survey called the Norwegian Mother, Father, and Child Cohort Study, Nature reported. They examined more than 21,000 responses from postmenopausal, perimenopausal, and nonmenstruating premenopausal women. Some were on long-term hormonal contraceptives.
They learned that 252 postmenopausal women, 1,008 perimenopausal women, and 924 premenopausal women reported having unexpected vaginal bleeding.
About half said the bleeding occurred within 4 weeks of the first or second shot or both. The risk of bleeding was up three to five times for premenopausal and perimenopausal women, and two to three times for postmenopausal women, the researchers found.
Postmenopausal bleeding is usually serious and can be a sign of cancer. “Knowing a patient’s vaccination status could put their bleeding incidence into context,” said Kate Clancy, a biological anthropologist at the University of Illinois at Urbana-Champaign.
The study received funding through the Norwegian Institute of Public Health and Research Council of Norway. The researchers reported no conflicts of interest.
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