Study: COVID vaccines linked to menstrual period changes, breakthrough bleeding

A new study by researchers in the USA shows that persons reported experiencing heavier bleeding during menstruation after receiving COVID vaccines.

The researchers from the University of Illinois at Urbana-Champaign and the Washington University in St. Louis School of Medicine received responses from over 35,000 participants who were “were vaccinated with Pfizer (N = 21,620), Moderna, (N = 13,001), AstraZeneca (N = 751), Johnson & Johnson (N = 3469), Novavax (N = 61), or other (N = 204) vaccines, with 23 not reporting vaccine type”.

The respondents vaccinated with the Johnson & Johnson doses were, however, later excluded from the study, considering that it was the only vaccine that was administered as a single dose at the time.

According to the study published on July 15 in Science Advances, respondents reported differences in their periods, while breakthrough bleeding was also reported by persons who were in post-menopause — not experienced menstruation for up to a year —  as well as persons who were on contraceptives that “eliminates menstruation”.

“Respondents reported noticing changes to their period 1 to 7 days after vaccines (dose 1: 31.4%; dose 2: 37.0%), 8 to 14 days after vaccines (dose 1: 25.9%; dose 2: 23.6%), or more than 14 days after receiving their vaccines (dose 1: 29.9%; dose 2: 26.8%), with the rest of respondents reporting that they were menstruating when they received the vaccine (dose 1: 12.7%; dose 2: 12.5%),” the study reads.

“In total, 42.1% reported heavier menstrual flow after vaccines, 14.3% reported not heavier (characterized by a mix of lighter or no change) menstrual flow, and 43.6% reported no change to flow after vaccines.”

The researchers, however, noted that the study is also to offer some insight into understanding concerns related to menstruation involving persons vaccinated against COVID.

“Respondents in our sample who menstruate regularly were about equally likely to have no bleeding changes after vaccination at all or to have heavier periods after vaccination. A much smaller proportion of people had lighter periods,” the article reads.

“Greater than a third of respondents who used gender-affirming hormone treatments experienced breakthrough bleeding after vaccination. The majority of premenopausal respondents on long-acting reversible contraceptives (LARC) and the majority of postmenopausal respondents experienced breakthrough bleeding as well.

“Among regularly menstruating respondents, those who had heavier bleeding after vaccine were more likely to be older, be Hispanic/Latinx, have experienced fever and/or fatigue side effects, have a lighter typical menstrual flow, have been pregnant, and/or have given birth. Regularly menstruating people with endometriosis, menorrhagia, fibroids, and PCOS were slightly more likely to experience heavier bleeding.

“Among nonmenstruating premenopausal respondents, those with breakthrough bleeding after vaccine were more likely to have been pregnant and/or given birth. Last, among postmenopausal respondents, those with breakthrough bleeding after vaccine were more likely to be younger and/or be Hispanic/Latinx.

“The nature of this survey means that we cannot compare the incidence of different experiences here with the general population (meaning, 40% of this sample having an experience does not mean that is the rate of that experience out in the world). The associations described here are not causal but provide evidence to better study these trends further. We emphasize that menstrual bleeding changes of this nature are generally not indicative of changes to fertility.”