There is growing evidence of small changes in the menstrual cycle in some women after receiving their COVID-19 vaccines, according to Herald Sun.

In the United States, at least 6,000 women have reported that they had their periods earlier than usual. In the United Kingdom, as many as 35,000 women experiencing menstrual changes.

However, there is no scientific evidence that links period irregularities to the COVID-19 vaccines.

A spokeswoman for Australia’s Department of Health told, “There is no link between the Covid-19 vaccines and changes in women’s menstrual cycles. The TGA [Therapeutic Goods Administration] has conducted a review into COVID-19 vaccines and menstrual disorders in response to increased reporting of these events in Australia and internationally.”

Currently, there is no proven link, but Dr. Victoria Male of Imperial College London said the period irregularities after vaccination should be further investigated.

Dr. Male wrote in The British Medical Journal, “Primary care clinicians and those working in reproductive health are increasingly approached by people who have experienced [changes to periods and unexpected vaginal bleeding] shortly after vaccination.”

“Most people who report a change to their period after vaccination find that it returns to normal the following cycle and, importantly,” she added, “there is no evidence that COVID-19 vaccination adversely affects fertility.”

Small changes in the menstrual cycle have been reported after receiving Pfizer, Moderna, and AstraZeneca vaccines, which “suggests 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,” Dr. Male said.

In April, Dr. Michelle Wise of the University of Auckland wrote in The Conversation, “In theory, a vaccine could affect a woman’s period. A vaccine is meant to induce an immune response in the body, and this immune response could have an impact on the menstrual cycle.”

“The [menstrual] cycle is mediated in part by the immune system,” she added. “For example, certain immune cells … are found in the endometrial lining, and involved in the shedding of the lining of the uterus during the menstrual cycle, and rebuilding it for the next cycle.”

“So it’s possible receiving a vaccine and having the expected immune response could affect the complex interplay between immune cells and signals in the uterus, and lead to the next period being heavier, more painful, or longer.”

Dr. Male said there have been false claims that are driving vaccine hesitancy among young women.

She said, “Vaccine hesitancy among young women is largely driven by false claims that COVID-19 vaccines could harm their chances of future pregnancy. Failing to thoroughly investigate reports of menstrual changes after vaccination is likely to fuel these fears.”

“If a link between vaccination and menstrual changes is confirmed, this information will allow people to plan for potentially altered cycles,” Dr. Male added. “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.”