Some women have reported changes to their menstrual cycle – including early or late periods – after taking a COVID-19 vaccine, but experts say these are normal reactions and are temporary side effects that do not affect fertility or the reproductive system in the long-term.
Read the latest updates in our dedicated coronavirus section.
“Data are reassuring that there is no effect on fertility and the effects on menstrual cycle are limited and for a few cycles, with no long-term implication,” Doctor Faysal al-Kak, an obstetrician (ObGyn) at the American University Beirut (AUB) Medical Center, told Al Arabiya English.
In addition to delayed or early starts, some women have reported symptoms including spotting, severe cramping, heavier than usual flows and “prolonged menstruation,” the doctor added.
“This was common across all vaccines” after the first or second dose, al-Kak said.
Why do women experience such symptoms after vaccines?
It is common for women to experience such symptoms and changes to their menstrual cycles after getting vaccinated against any virus, not just the coronavirus, according to the doctor. Official research has yet been done on the correlation between COVID vaccines specificially and changes to periods.
Al-Kak went on to explain how vaccines building up immunity in the body can affect a woman’s period, just how any other stressors – including travel, diet changes, and stress – affect the master gland in the brain which controls menstruation.
“Looking at the mechanism of action of vaccines in general, which is basically to build up an immune reaction and protection against the pathogen or germ – which implies the release of immunogenic defense substances – this process will affect the changes happening across the menstrual cycle and ovulation at the lining of the endometrium [the cavity of uterus],” the AUB doctor said.
Read also: Researchers to study whether COVID-19 vaccines affect women’s periods
A woman’s average 28-day menstrual cycle includes hormonal interplay, thickening of internal uterine lining followed by ovulation, and then either menses or fertilization of an egg. Immune cells play a role in in the different stages the uterus goes through to either prepare for pregnancy, or a period if the egg is not fertilized.
According to al-Kak, “all these processes require local inflammatory reaction and thus release of inflammatory substances.”
Taking a vaccine initiates an immune reaction, according to the doctor. This includes the release of inflammatory substances which will interfere with those associated with the “stability of the endometrial lining and ovulation, leading to weakening support and early shedding of endometrial lining causing premenstrual spotting and earlier menses [period], and midcycle spotting,” al-Kak explained.
Research on connection between vaccines, periods underway
According to a New York Times report published Tuesday, yearlong studies will be conducted “to examine any possible connections between vaccination and irregular menstruation.” The studies are reportedly backed by funding from the National Institute of Health.
Teams from Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University, and Oregon health will conduct the research on unvaccinated individuals.
“The studies will include participants of all ages and backgrounds who have not yet been vaccinated, including those who plan to get the shots and those who do not, in order to study their menstrual cycles before and afterward,” the New York Times reported.