A recent study found that a substantial number of menstruating people in its sample experienced unusual menstrual bleeding after getting the COVID-19 vaccine.
Its publication follows past debate over whether vaccination against COVID-19 negatively affected women’s fertility. While an earlier study in February suggested that there is no direct link between the COVID-19 vaccine and infertility, it did not examine whether there was a correlation between vaccination and menstruation irregularities.
Researchers at the University of Illinois at Urbana-Champaign and Washington University School of Medicine in St. Louis decided to look into this potential correlation by distributing an online survey to tens of thousands of people.
The study reported that after receiving the COVID-19 vaccine:
“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.”
This is the largest study so far on the correlation between the vaccine and menstrual cycles. The participants were between the ages of 18 and 80, fully vaccinated with a U.S.-approved COVID-19 vaccine, and had not previously contracted the virus.
According to the analysis, individuals had a higher chance of experiencing heavier bleeding when they had used hormonal contraception, had previously been pregnant, or had been diagnosed with certain reproductive conditions like polycystic ovarian syndrome or fibroids.
Additionally, individuals who experienced side effects after receiving the vaccine, such as fatigue and fever, were at a higher risk of abnormal bleeding during their periods.
Furthermore, bleeding was reported by participants in the study that had not been menstruating regularly, including transgender men, postmenopausal women, and people using long-acting reversible contraceptives like birth control implants and intrauterine devices (IUDs).
According to Dr. Alison Edelman, Oregon Health and Science University professor, “Menstrual cycles are not perfect clocks.” Some variation in a person’s cycle is not necessarily concerning.
Many factors contribute to changes in the menstrual cycle, such as weight loss, weight gain, stress and illness, calorie restriction, infections, and exercise.
The research team emphasized that the study does not support any connection between infertility and the vaccine.
“The uterine reproductive system is flexible and adaptable in the face of stressors to weather short-term challenges in a way that leaves long-term fertility intact,” their report stated, noting these short-term changes do not indicate long-term effects.
Though there have been few studies on the correlation between vaccines and menstruation, other vaccines have caused irregular menstruation, such as the typhoid vaccine and the Hepatitis B vaccine.
The report sets forward the idea that “systemic inflammatory responses may in some individuals invoke downstream responses in target organs such as the uterus,” causing menstrual irregularities.
