Vaginal bleeding after COVID-19 vaccination among non-menstruating women
Women who do not menstruate due to menopause or hormone use reported increased frequency of unexpected vaginal bleeding after COVID-19 vaccination, according to a new study from the Norwegian Institute of Public Health (NIPH).
Previous studies from NIPH (Population-based cohort study in Norway and Heavy bleeding and other menstrual disturbances in young women after COVID-19 vaccination) observed a higher risk of menstrual disturbances after COVID-19 vaccination among younger women.
This new study also finds a higher frequency of unexpected vaginal bleeding in the time after receiving a COVID-19 vaccine among women who do not menstruate.
“In this study, we have documented the responses from a large sample of women who were asked about unexpected vaginal bleeding shortly after vaccination,” says Kristine Blix, a medical doctor and researcher at the Norwegian Institute of Public Health.
A total of 22,000 women in the Senior Cohort and the Norwegian Mother, Father and Child Study (MoBa) were asked if they had experienced unexpected vaginal bleeding in 2021, the year when the vast majority received their first COVID-19 vaccine dose.
“In the new study, we found an increased risk of unexpected vaginal bleeding among women who are no longer menstruating due to menopause, as well as those who do not menstruate because they use hormones,” says Blix.
- Among 7725 postmenopausal women, 252 women (3.3 %) reported unexpected vaginal bleeding. Almost half of these women (1.5 %) reported bleeding in the month after taking the COVID-19 vaccine.
- Among 7148 perimenopausal (undergoing menopause) women, 1008 women (14.1 %) reported unexpected vaginal bleeding. Half of these women (7.2 %) reported bleeding in the month after taking the COVID-19 vaccine.
- Among 7052 non-menstruating premenopausal women (before menopause), 924 women (13.1%) reported unexpected vaginal bleeding. Just over half of these women (7.3%) reported bleeding in the month after taking the COVID-19 vaccine.
- The premenopausal women who did not menstruate were mainly using hormonal intrauterine devices (IUDs) (74%).
“When we enter these figures into a statistical model that also takes into account that the time before vaccination is longer than the time after vaccination, we can estimate whether the risk is increased in the time after vaccination, and how much it is increased compared to the risk before the vaccine,” explains Blix.
"Assuming that the women recalled all bleeding episodes equally well, that is, that they did not over-report bleeding after vaccination, or, more importantly perhaps, did not under-report bleeding before vaccination, the risk is increased 2-4 times in the first month after vaccination," adds Blix.
These figures differ slightly for the three groups of women:
- For postmenopausal women, we find a 2-3 fold increased risk in the first month after vaccination
- For menopausal women, we find a 3-4 fold increased risk in the first month after vaccination
- For premenopausal women, we find an approximate 4-fold increased risk in the first month after vaccination
Most of the women were vaccinated with an mRNA vaccine (Comirnaty from Pfizer-BioNTech or Spikevax from Moderna). The researchers found an increased risk after both the vaccines. For premenopausal women, the risk was somewhat higher after Spikevax compared to Comirnaty.
Among women who reported bleeding in the month after the 1st or 2nd vaccine dose:
- the vast majority (75 – 85 %) reported bleeding that lasted a week or less. The distribution was as follows for the three groups:
- Postmenopausal women: 76 %
- Perimenopausal women: 75 %
- Premenopausal women: 85 %
- the bleeding was described as heavy for between 22 - 33%. The distribution was as follows for the three groups:
- Postmenopausal women: 22 %
- Perimenopausal women: 33 %
- Premenopausal women: 22 %
- 20% of postmenopausal women reported that they had consulted a doctor for vaginal bleeding disturbances or abdominal pain during the study period. Corresponding proportions for peri- and premenopausal women were 9 and 4.5% respectively.
- In comparison, 44 %, 21 % and 19 % of post-, peri- and pre-menopausal women who experienced bleeding before vaccination reported that they consulted a doctor.
The analyses are based on the first and second vaccine dose.
Among those who experienced bleeding in the month after the first dose, a total of 1.9 % stated that the bleeding lasted for longer than four weeks.
Bleeding disturbances have not been linked to vaccination in the past, and such events were not addressed in the randomised clinical trials of the COVID-19 vaccines. In this study, the researchers documented how participants in the Senior Cohort and MoBa responded when asked about unexpected vaginal bleeding shortly after vaccination.
“Among non-menstruating women who reported bleeding after vaccination, most reported having a single bleeding episode, that the bleeding lasted for a week or less, and that the bleeding was not heavy,” says Blix.
She emphasises that it is reassuring that others who analyse diagnoses from patient registries find little excess risk after vaccination. This may reflect that such episodes are mild and self-limiting, and are generally not experienced as very concerning.
The researchers also observed that women who had experienced unexpected bleeding after vaccination reported that they had consulted a doctor to a lesser extent than women who had experienced this at other times. This may have an impact on how studies based on registered diagnoses in the healthcare system are interpreted.
The Norwegian Institute of Public Health has previously shown that there was an increased risk of menstrual disturbances among young girls and women from the age of 12 and over:
- Increased risk of menstrual disturbances after COVID-19 vaccination in girls aged 12-15
- Increased risk of menstrual disturbances in young women after COVID-19 vaccination
Following an overall assessment from the pharmaceutical authorities, heavy menstrual bleeding was included as a possible side effect in the product information for the mRNA vaccines in October 2022. Whether the pharmaceutical authorities will consider unexpected vaginal bleeding among non-menstruating women as a possible side effect has not been decided. Such evaluations are based on an overall assessment of all relevant studies and other available information. More studies are needed, and these events should be investigated as part of future clinical trials for new and variant vaccines.
Weaknesses of the study
The study is based on questionnaire data, where women have provided information about events going back in time. The study cannot therefore identify a definite causal relationship between COVID-19 vaccination and unexpected vaginal bleeding.
“It is possible that women have better recollection of what happened after vaccination, and that the association appears stronger than it actually is,” explains Kristine Blix, lead author of the study.
Although the participants cannot have consented to the study because they experienced bleeding after vaccination (they were recruited before vaccination began), it cannot be ruled out that some women may have chosen to complete this questionnaire because they had an unusual experience after vaccination.
"Such bias can lead to the association being overestimated, and should be considered when interpreting the results," says Blix.
Must consult a doctor
Bleeding disturbances are common among young girls, during pregnancy, with hormone use and in the time around menopause, and can have many causes. Women who experience unexpected vaginal bleeding should evaluate whether to consult a doctor, regardless of vaccination. Women who experience persistent bleeding should contact a doctor. Importantly, women who experience postmenopausal bleeding should always consult a doctor to rule out other conditions such as uterine cancer, or precursors to cancer.
Reported side effects and other studies
All data on COVID-19 vaccines and vaginal bleeding come from observational studies conducted after the vaccines were launched. Two studies on postmenopausal bleeding diagnosed and registered in the healthcare system before and after the COVID-19 vaccine found a slight excess risk of such diagnoses in the period after vaccination, compared to the period before.
- Suh-Burgmann et al., Association between vaccination against COVID-19 and postmenopausal bleeding, AJOG, 2022
- Ljung et al., Association between SARS-CoV-2 vaccination and healthcare contacts for menstrual disturbance and bleeding in women before and after menopause: nationwide, register based cohort study, BMJ, 2023
The Norwegian Medicines Agency and spontaneous reporting systems in other countries have received reports of bleeding disturbances among women after COVID-19 vaccination. Heavy menstrual bleeding was included as a possible side effect in the product information for the mRNA vaccines in October 2022. Other disturbances such as vaginal bleeding in postmenopausal women have also been reported, but to a lesser extent:
- COVID-19 vaccines and menstrual disturbances - Norwegian Medicines Agency
- Postmenopausal bleeding after administration of COVID-19 vaccines. Netherlands Pharmacovigilance Centre Lareb
Why is this happening?
Blix explains that the potential biological mechanisms are unknown, but may be linked to viral properties, the mRNA platform that the vaccines use or other vaccine components.
“The contribution from the participants in the study is extremely important and provides unique knowledge about conditions that cannot be obtained from health registries. We are extremely grateful for the effort and perseverance shown by participants throughout the pandemic,” she concludes.