Pfizer, Moderna COVID vaccines associated with severe vaginal bleeding in women 45 and up: study

Highest risks in postmenopausal women after booster, Swedish researchers say in study of nearly 3 million women. Smaller increased risk for premenopausal women.

Published: May 23, 2023 12:44pm

Updated: May 23, 2023 12:48pm

Women 45 and older who took Pfizer and Moderna mRNA COVID-19 vaccines have a notably higher risk of vaginal bleeding severe enough to prompt a medical visit after a booster, according to a new study.

The study included nearly 3 million diagnosed Swedish women ages 12-74 and was published in the British Medical Journal.

The increased risk of bleeding and "menstrual disturbance" was smaller for premenopausal women (ages 12-49) in the study, which excluded women with a "history of any menstruation or bleeding disorders" among other conditions.

About 88% of the women had at least one vaccine dose, and among those, 64% received a third dose.

The adjusted hazard ratio for postmenopausal bleeding after any dose, when including covariates, 1-7 days after vaccination was 1.12 and 8-90 days later was 1.14, meaning 12% and 14% increased risk, respectively, compared to unvaccinated women. Those jumped to 25% and 28% increased risk after the booster in the 1-7 and 8-90 day windows, respectively.

The picture is less clear for the younger group, however. When including covariates, the increased risk for menstrual disturbance after any dose was 13% (1-7 days) and 6% (8-90 days). The highest risk was 1-7 days after the first dose (26%). Increased risk of premenopausal bleeding was greatest 1-7 days after the first and third doses, both 14%. 

The risks were notably higher for younger women in the "crude model," which did not include covariates that may have raised their risk unrelated to vaccination.

"These findings do not provide substantial support for a causal association between SARS-CoV-2 vaccination and healthcare contacts related to menstrual or bleeding disorders," the researchers claimed, which puzzled former New York Times drug industry reporter Alex Berenson.

"Because of its size and reliance on formal medical diagnoses rather than self-reporting of vaginal bleeding, the study offers the strongest evidence yet that the connection between Covid shots and bleeding is real," Berenson wrote in his newsletter. "This study drew on an enormous database and had no sampling bias since almost all Swedish women were included."

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