Pfizer, Moderna and AstraZeneca’s Covid vaccines cause unexpected vaginal bleeding in older women and women on birth control, a study has confirmed.
While changes in bleeding and periods in menstruating women following vaccination have been known for years, few studies have looked at the effects on women who do not normally menstruate, such as the elderly and women taking contraceptives.
However, a new study examining data from more than 20,000 women in this category found that the risk of vaginal bleeding increased two to three times in the four weeks after Covid vaccination compared to before vaccination.
The risk was three to five times higher in menopausal and premenopausal women.
The researchers examined data from August and September 2021.
98 percent of included women reported receiving their Covid vaccinations in January 2021, meaning they had received the original Covid vaccine and not updated booster shots.
Experts aren’t entirely sure why changes in menstruation occur, but some believe the vaccine causes some body tissues to become inflamed, leading to changes in the lining of the uterus and hormone levels throughout the body
Vaginal bleeding in postmenopausal women can be a sign of a serious condition such as cancer, and in this group more women than the others sought medical attention after experiencing unexplained bleeding – 30.6 percent
In addition, in Norway, where the data was collected, Covid vaccines manufactured by Moderna, Pfizer-BioNTech and AstraZeneca, among others, were used.
When Covid vaccines were first rolled out, tens of thousands of women complained of late or unusually heavy periods.
Before formal research was conducted, anti-vaxxers seized on the reports and used them to incite fear among Americans that the vaccines caused infertility.
However, research published later showed that although there are menstrual changes after the Covid vaccination, they are minor, temporary and have no impact on fertility.
Experts aren’t entirely sure why changes in menstruation occur, but some believe the vaccine causes some body tissues to become inflamed, leading to changes in the lining of the uterus and hormone levels throughout the body.
While the current study didn’t examine why these women experienced unexplained vaginal bleeding, sometimes called breakthrough bleeding, scientists suspected it might be related to the spike protein used in the shots.
Study author Kristine Blix from the Norwegian Institute of Public Health in Oslo said: “We had already sent out bi-weekly questionnaires to cohort participants at the beginning of the pandemic to monitor the effects of the pandemic.”
“In the first COVID-19 vaccination questionnaire sent in 2021, some women indicated in free text fields that they had heavy menstrual bleeding.
“That led us to ask about bleeding patterns in a structured way.”
What is normal for a period?
A period is the part of the cycle in which a woman bleeds from her vagina for a few days.
For most women this happens about every 28 days, but it is not uncommon for individual women’s cycles to be between 21 and 40 days.
The period usually lasts between three and eight days, with an average of five.
Bleeding is usually heaviest in the first two days.
Some women have irregular periods where the cycle is inconsistent.
For some this is normal and nothing to worry about, but the NHS advises women to contact their GP if:
- if your period suddenly becomes irregular and you are under 45 years old
- Your period comes more often than every 21 days and less often than every 35 days
- Your period lasts longer than seven days
- There is a difference of at least 20 days between the shortest and longest menstrual cycles
Researchers examined data from nearly 22,000 women who had already experienced menopause, women in perimenopause, the period just before entering menopause, and non-menstruating premenopausal women, including some who were on long-term hormonal contraception.
They found that 252 postmenopausal women (3.3 percent), 1,008 perimenopausal women (14.1 percent), and 924 premenopausal women (13.1 percent) reported unexplained or breakthrough vaginal bleeding throughout 2021.
Of the women who reported this, about half in each group said their bleeding occurred within four weeks of the first and/or second dose of the vaccine.
The data showed: 45 percent of postmenopausal women, 51 percent of perimenopausal women and 55 percent of premenopausal women reported unexplained bleeding.
Of these women, 28 percent of the perimenopausal women described the bleeding as heavy, compared to 18 percent of the two postmenopausal women who had not yet experienced menopause.
Women in the study’s older cohort were between 61 and 88 years old and were considered non-menstruating. Other nonmenstruating women were 32 to 64 years old. Respondents were then divided into the three menopause categories.
Vaginal bleeding in postmenopausal women can be a sign of a serious condition such as cancer, and more women in this group than the others sought medical attention after unexplained bleeding – 30.6 percent compared to 13.8 percent for perimenopausal women and 9, 3 percent in premenopausal women.
The risk of breakthrough bleeding in the first four weeks after a dose of Moderna’s vaccine was associated with a 32 percent increase compared to the Pfizer-BioNTech vaccine.
Heavy menstrual bleeding has now occurred as a side effect of the vaccination.
The study, published this week in the journal Science Advances, analyzed data from an ongoing health survey called the Norwegian Mother, Father, and Child Cohort Study.