Researchers in Norway have found that women who don’t menstruate – including post-menopausal 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.
When Covid-19 jabs were rolled out globally, many women reported heavier-than-usual menstrual bleeding soon after vaccination, and 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 – those taking contraceptives or who have been through menopause.
The work is published in Science Advances.
The team did not investigate the reasons for the unexplained bleeding, but suggested it could be linked to the SARS-CoV-2 spike protein used in the vaccines.
Blix and colleagues used an ongoing population health survey called the Norwegian Mother, Father and Child Cohort Study.
“From early in the pandemic, we already had bi-weekly questionnaires going out to cohort participants to monitor its effects,” she said.
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 added.
Widespread effect
The team looked at more than 21 000 responses from post-menopausal, peri-menopausal and non-menstruating pre-menopausal women, including some who were on long-term hormonal contraceptives.
The results were surprising, said Blix. They found that 252 post-menopausal women, 1 008 peri-menopausal and 924 pre-menopausal women reported 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.
Pre-menopausal and peri-menopausal 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 post-menopausal 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 pr-cancerous 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,” said Kate Clancy, a biological anthropologist at the University of Illinois Urbana-Champaign.
Clancy’s group has published results of their own survey showing changes in menstrual bleeding after Covid-19 vaccination. She said the results aligned 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,” Blix said.
Study 1 details
Unexpected vaginal bleeding and COVID-19 vaccination in non-menstruating women
Kristine Blix, Ida Laake, Lill Trogstad, et al.
Published in Science Advances on 22 September 2023
Abstract
The association between coronavirus disease 2019 (Covid-19) vaccination and vaginal bleeding among non-menstruating women is not well studied. The Norwegian Institute of Public Health followed several cohorts throughout the pandemic and early performed a systematic data collection of self-reported unexpected vaginal bleeding in non-menstruating women. Among 7725 post-menopausal women, 7148 peri-menopausal women, and 7052 pre-menopausal women, 3.3, 14.1, and 13.1% experienced unexpected vaginal bleeding during a period of 8 to 9 months, respectively. In post-menopausal women, the risk of unexpected vaginal bleeding (i.e., post-menopausal bleeding) in the 4 weeks after Covid-19 vaccination was increased two- to threefold, compared to a pre-vaccination period. The corresponding risk of unexpected vaginal bleeding after vaccination was increased three- to fivefold in both non-menstruating peri- and premenopausal women. In the premenopausal women, Spikevax was associated with at 32% increased risk as compared to Comirnaty. Our results must be confirmed in future studies.
Study 2 details
Investigating trends in those who experience menstrual bleeding changes after SARS-CoV-2 vaccination
Katharine Lee, Eleanor Junkins, Kathryn Clancy, et al.
Published in Science Advances on 15 July 2022
Abstract
Early in 2021, many people began sharing that they experienced unexpected menstrual bleeding after SARS-CoV-2 inoculation. We investigated this emerging phenomenon of changed menstrual bleeding patterns among a convenience sample of currently and formerly menstruating people using a web-based survey. In this sample, 42% of people with regular menstrual cycles bled more heavily than usual, while 44% reported no change after being vaccinated. Among respondents who typically do not menstruate, 71% of people on long-acting reversible contraceptives, 39% of people on gender-affirming hormones, and 66% of postmenopausal people reported breakthrough bleeding. We found that increased/breakthrough bleeding was significantly associated with age, systemic vaccine side effects (fever and/or fatigue), history of pregnancy or birth, and ethnicity. Generally, changes to menstrual bleeding are not uncommon or dangerous, yet attention to these experiences is necessary to build trust in medicine.
COVID vaccines linked to unexpected vaginal bleeding (Open access)
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