Two studies have confirmed a link between the Covid-19 vaccine and periods

Since the rollout of the Coronavirus vaccine in the UK, many people have shown concerns about the jab’s impact on their period. In fact, over 36,000 people have reported period irregularities after getting the vaccine, as per the MHRA Yellow Card scheme, including bleeding earlier than expected (often shortly after the vaccine), spotting, heavier bleeds or painful periods.

However, a new study funded by the National Institute of Health (NIH) in the US, has found that the Covid-19 vaccine was associated with a less than one-day change in menstrual cycle length for both vaccine-dose cycles, compared with pre-vaccine cycles.

The International Federation of Gynecology and Obstetrics classifies a variation in cycle length as normal if less than 8 days. Diana W. Bianchi, M.D., director of Eunice Kennedy Shriver National Institute of Child Health and Human Development, said: “It is reassuring that the study found only a small, temporary menstrual change in women.

“These results provide, for the first time, an opportunity to counsel women about what to expect from COVID-19 vaccination so they can plan accordingly.”

However, the study noted that questions still remain about other possible changes in menstrual cycles, such as “menstrual symptoms, unscheduled bleeding, and changes in the quality and quantity of menstrual bleeding.”

Another study, conducted by the Norwegian Institute of Public Health, collected reports of menstrual disturbances from 5688 women aged 18-30 years and examined the occurrence of such disorders before and after both the first and second doses of the vaccine.

The study concluded that “menstrual disturbances were generally common regardless of vaccination,” adding that there was a “significant increase in menstrual disturbances after vaccination, particularly for heavier bleeding than usual, longer duration and for short interval between menstruations.”

The authors also noted that bleeding disturbances in general, as well as endocrine alterations, may underlie these findings. 

The British Medical Journal (BMJ) reports “The findings from both these studies are reassuring: changes to the menstrual cycle do occur following vaccination, but they are small compared with natural variation and quickly reverse.” 

The BMJ has also cautioned against extrapolating these findings to those who received their vaccinations in the UK, explaining that, “Unlike the US and Norway, where the interval between the first two vaccine doses is 3-4 weeks, the interval in the UK is 8 weeks. 

“Under the UK vaccination schedule, it is therefore impossible to receive both doses of the vaccine in the same cycle, and this may mean that the changes observed in the US and Norway do not occur here.”

“In the interim,” the BMJ advises, “the [Medicines and Healthcare products Regulatory Agency] says that current evidence does not support a link between changes to menstrual periods and covid vaccination in the UK.”

Reproductive immunologist Dr. Victoria Male of Imperial College London, has previously called for “robust research” into menstrual changes after Covid-19 vaccinations, writing in the BMJ: