Dutch medicines monitoring agency Lareb has received nearly 9,400 reports of heavy menstrual bleeding from women who have been given Pfizer/BioNTech and Moderna coronavirus vaccines, the agency said on Friday.

By far the most were about the Pfizer/BioNTech product, but this is also the most widely used vaccine in the Netherlands, Lareb said.

On Friday, the European Medicines Agency said it was recommending that heavy menstrual bleeding should be added to the product information as a side effect of unknown frequency with the two vaccines.

Cases of heavy menstrual bleeding have been reported after the first, second and booster doses of Comirnaty and Spikevax, the Amsterdam-based EMA said.

The data mostly involved cases which appeared to be non-serious and temporary in nature, the EMA said, adding that ‘menstrual disorders in general are quite common and they can occur for a wide range of reasons’.

There is no evidence to suggest the menstrual disorders experienced by some women have any impact on reproduction and fertility, the agency said.

Research

Lareb, meanwhile, is conducting further research on the number of women experiencing menstrual disorders before and after the covid vaccination based on data from family doctors.

In total, the agency has had over 27,000 reports of menstrual side effects after vaccination, ranging from delays, to heavier or lighter blood loss and period pains.

Lareb said last year that menstrual irregularities are common and can also be caused by infections, sickness and stress. ‘It is not clear yet if menstrual irregularities are a side effect of the corona vaccines, but this is a possibility,’ it added. ‘The vaccine stimulates the immune system and this can affect hormone levels.’