NATURE – 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 study 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.
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.
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“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.