Research Urged Into Link Between COVID Vaccines and Menstrual Changes

Peter Russell

September 16, 2021

Editor's note, 16 September 2021: This article was updated with a statement from the MHRA.

A suspected link between COVID-19 vaccines and menstrual changes is "plausible" and should be investigated, a UK reproductive specialist has said.

Changes to periods and unexpected vaginal bleeding are not listed among common side effects by the Medicines and Healthcare products Regulatory Agency (MHRA).

However, Dr Victoria Male, PhD, lecturer in reproductive immunology at Imperial College London (ICL), said clinicians were increasingly hearing from women who have experienced these events shortly after being vaccinated.

In fact, more than 30,000 reports of menstrual change had been made using the MHRA's yellow card surveillance scheme by September 2, 2021, she wrote in an editorial in The BMJ.

The reports were not confined to one particular vaccine and were applicable to both mRNA vaccines, such as Pfizer/BioNTech, and adenovirus vectored vaccines, such as AstraZeneca/Oxford.

Furthermore, natural infection with the SARS-CoV-2 virus was also likely to be associated with menstrual changes, Dr Male said. In a study last year, published in Reproductive Medicine Online.  28% of women infected with the virus experienced menstrual disruption.

Menstrual Change and Immune Response

That suggested "it is likely to be a result of the immune response to vaccination rather than a specific vaccine component", said Dr Male, noting that vaccination against human papillomavirus (HPV) was also associated with menstrual changes.

However, most women find that their period returns to normal the following cycle, she said. Critically, there was no evidence that COVID vaccination affected fertility.

Dr Male argued that "robust research" into possible adverse reactions was needed to drive down vaccine hesitancy among women concerned by false claims that accepting a vaccine could impair their fertility.

A failure to investigate was likely to "fuel these fears", while clear and trusted information would allow women "to predict their menstrual cycles to either achieve or avoid pregnancy".

She pointed out that the US National Institutes of Health recently awarded a grant of £1.2 million for research into a link between vaccination and changes in menstruation.

In the meantime, Dr Male suggested that clinicians encourage their patients to report any changes to periods or unexpected vaginal bleeding after vaccination to the MHRA's scheme. Also, that anyone reporting a change in periods persisting over a number of cycles, or new vaginal bleeding after the menopause, should be managed according to the usual clinical guidelines for those conditions.

"One important lesson is that the effects of medical interventions on menstruation should not be an afterthought in future research," she said.

Also, bleeding "should be actively solicited in future clinical trials, including trials of COVID-19 vaccines", Dr Male said.

The Royal College of Obstetricians and Gynaecologists (RCOG) backed the call for more research into the issue.


Dr Jo Mountfield, RCOG vice president, commented: "We understand that any changes to periods following a COVID-19 vaccine can be concerning. 

"We want to reassure women that any changes generally revert back to normal after one or two cycles. We would encourage anyone who experiences heavy bleeding that is unusual for them, especially after the menopause, to speak to a healthcare professional.

"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."

Dr Alison Cave, MHRA chief safety officer, commented: "We are closely monitoring reports of suspected menstrual disorders following COVID-19 vaccination. 
"Coronavirus Yellow Card is a robust system for collection of information on the safety of vaccines, enabling our assessors to rapidly evaluate emerging safety signals.  As outlined in our vaccine safety surveillance strategy, the Yellow Card scheme is one of several sources of evidence we use when evaluating the safety of vaccines. 
"Based on our current rigorous safety monitoring, women can be reassured that the current evidence does not show a link with any changes in women’s periods or symptoms, nor is there any evidence to suggest that COVID-19 vaccines will affect fertility. This is also the conclusion of our expert scientific advisory committee, the Commission on Human Medicines."

Menstrual changes after covid-19 vaccination. BMJ 2021; 374 doi: (Published 16 September 2021)


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