While changes in bleeding and periods in menstruating women post-shot have been known for years, few studies have looked at the impact on women who don’t normally menstruate, such as the elderly and those on birth control.
But a new study – that looked at data from more than 20,000 women in this category – found the risk of vaginal bleeding increased two to three times in the four weeks after Covid vaccination compared to before the shot.
In women entering menopause and premenopausal women, the risk was three to five times higher.
Researchers looked at data from August and September 2021.
Ninety-eight percent of the women included reported receiving their Covid vaccines in January 2021, meaning they had received the original Covid vaccine as opposed to any updated booster shots.
Additionally, in Norway, where the data was collected from, Covid vaccines used included those manufactured by Moderna, Pfizer-BioNTech and AstraZeneca.
When Covid vaccines were first rolled out, tens of thousands of women complained about late or unusually heavy periods.
Before formal research was conducted, anti-vaxxers latched onto the reports and used them to infuse fear in Americans that the vaccines caused infertility.
However, research later released showed while menstrual changes do occur following Covid vaccination, they are minor, temporary and do not impact fertility.
Experts are not entirely sure why changes in menstruation occur, but some believe the vaccine causes some of the body’s tissue to become inflamed, causing changes to the lining of the uterus and hormone levels throughout the body.
While the recent study did not investigate why these women experienced unexplained vaginal bleeding, sometimes referred to as breakthrough bleeding, scientists did suggest it could be linked 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, from the early pandemic, biweekly questionnaires going out to cohort participants to monitor effects of the pandemic.
‘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.’