The largest study to date with more than 35,000 participants – women and people of gender diversity – confirmed that 42% of women experienced an increase in menstrual bleeding within two weeks of vaccination against the covid.
In addition, the study describes for the first time the occurrence of spontaneous bleeding in a large number of people who have not had their period -because they have had menopause or because they were taking hormonal contraceptive treatment or for a sex change-, after having received the vaccine against SARS-CoV-2.
The conclusions of this study, published this Friday in the journal Scientists progressto confirm a side effect that had been reported by women and ignored by science and reveal that this effect of the vaccine affected “a significant number of people”.
However, the study data show that these alterations are temporary and are associated with certain triggers such as age, suffering from systemic side effects associated with the vaccine (fever or fatigue), or history of pregnancy and childbirth, among others.
“Menstruating and menstruating people began to report unexpected bleeding after receiving the vaccine in early 2021,” said US study researchers and leaders Katharine Lee of Tulane University and Kathryn Clancy of the University. University of Illinois at Urbana-Champaign.
In vaccine trials, menstrual cycles or bleeding are usually not questioned, so this side effect is often ignored or excluded from studies, despite the fact that some vaccines, such as those for typhoid fever, hepatitis B and HPV, can alter menstruation.
To do the study, the authors used a survey in which they asked people on their experiences after getting the covid vaccine.
The authors only included data from people who had not had covid (because the disease can cause menstrual changes) and excluded data from people aged 45 to 55 to avoid confounding the results. with menopause or previous changes.
Thus, the study focused on menstruating people, postmenopausal women and people on hormone therapies that suppress the cycle.
42.1% of respondents said they had heavier menstrual flow in the first two weeks after vaccination, 43.6% that their menstrual flow had not changed and 14.3% had experienced no change or , if any, less bleeding than usual.
The study found possible associations with a person’s reproductive history, hormonal status, demographics, and changes in menstruation after vaccination.
For example, respondents who had been pregnant were most likely to report heavier bleeding after vaccination, with a slight increase in those who had not given birth.
And more than 70% of respondents using long-acting reversible contraceptives and 38.5% of those taking gender-affirming hormone treatments reported this side effect.
Although menstrual disorders are not uncommon or dangerous, unexpected changes can be concerning.
“Unexpected intermittent bleeding is one of the first signs of certain cancers in people who are postmenopausal and those who use gender-affirming hormones,” says Lee.
This is why “this screening is very important in order to be able to detect cancers in time”, explains Clancy.
The authors reiterate, however, that getting vaccinated is one of the best ways to prevent covid, hospitalization and death.