But there’s also evidence the immune response prompted by both vaccines and viral infections can temporarily affect menstrual cycles, so studying these effects is important, Dr. Victoria Male, a reproductive specialist at Imperial College London, wrote in the BMJ.
“Vaccine hesitancy among young women is largely driven by false claims that Covid-19 vaccines could harm their chances of future pregnancy,” Male wrote.
“Failing to thoroughly investigate reports of menstrual changes after vaccination is likely to fuel these fears,” she added.
“If a link between vaccination and menstrual changes is confirmed, this information will allow people to plan for potentially altered cycles. Clear and trusted information is particularly important for those who rely on being able to predict their menstrual cycles to either achieve or avoid pregnancy.”
The US National Institutes of Health said last month it was spending $1.67 million to help five research teams study the potential effects of Covid-19 vaccines on menstruation.
“Numerous factors can cause temporary changes in the menstrual cycle, which is regulated by complex interactions between the body’s tissues, cells and hormones,” the NIH’s National Institute of Child Health and Human Development said in a statement issued August 30.
“Immune responses to a COVID-19 vaccine could affect the interplay between immune cells and signals in the uterus, leading to temporary changes in the menstrual cycle. Other factors that may cause menstrual changes include pandemic-related stress, lifestyle changes related to the pandemic, and infection with SARS-CoV-2 (the virus that causes COVID-19).”
Male said the indications were that these changes, if they occur, are temporary and harmless.
“Most people who report a change to their period after vaccination find that it returns to normal the following cycle and, importantly, there is no evidence that Covid-19 vaccination adversely affects fertility,” she wrote.
“Menstrual changes have been reported after both mRNA and adenovirus vectored covid-19 vaccines, suggesting that, if there is a connection, it is likely to be a result of the immune response to vaccination rather than a specific vaccine component,” she added.
“Vaccination against human papillomavirus (HPV) has also been associated with menstrual changes. Indeed, the menstrual cycle can be affected by immune activation in response to various stimuli, including viral infection: in one study of menstruating women, around a quarter of those infected with SARS-CoV-2 experienced menstrual disruption.”
But studying these effects should not be an afterthought, Male said.
Dr. Jo Mountfield, vice president of the UK’s Royal College of Obstetricians and Gynecologists, said it’s understandable women would be concerned about such changes.
“There is no evidence to suggest that these temporary changes will have any impact on a person’s future fertility, or their ability to have children. It is important to get vaccinated as the best protection against coronavirus. This is especially important if you are planning a pregnancy, as we know unvaccinated pregnant women are more at risk of becoming seriously ill from COVID-19,” Mountfield said in a statement.
“We support calls for more research to understand why women may be experiencing changes to their menstrual cycle after having the vaccine.”