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  • Menstrual changes following COVID-19 vaccination

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Menstrual changes following COVID-19 vaccination

There is an increase in the incidence of menstrual changes among young women after vaccination against coronavirus, according to initial findings from population studies by the Norwegian Institute of Public Health. The NIPH has advice for women who have experienced changes in menstruation after vaccination.

There is an increase in the incidence of menstrual changes among young women after vaccination against coronavirus, according to initial findings from population studies by the Norwegian Institute of Public Health. The NIPH has advice for women who have experienced changes in menstruation after vaccination.


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Early in summer 2021, the first reports came about women who were experiencing menstrual changes after vaccination against coronavirus. As a result, the NIPH added questions about menstrual changes to several ongoing population studies. The first results are now available for women aged 18-30 who are participants in the UngVoksen (Young Adult) cohort study.

"Menstrual changes are very common, and even before vaccination, almost four out of ten young women reported that they had experienced such changes. However, in this study we see that more women experienced changes after the first or second vaccine dose," says Dr Lill Trogstad, Project Leader at the Norwegian Institute of Public Health.

The main purpose of the study is to clarify whether menstrual changes occur more frequently among vaccinated than non-vaccinated women.

The results are published in the Social Science Research Network (SSRN):

Results from the first study

  • Almost 4 out of 10 women aged 18–30 years reported that they had experienced menstrual changes during their last period before vaccination.
  • Many women reported heavier periods than normal after the first and second vaccine dose:
    • 7.6 per cent reported heavier periods before vaccination
    • 13.6 per cent reported heavier periods after the first dose
    • 8.2 per cent reported heavier periods before the second dose
    • 15.3 per cent reported heavier periods after the second dose
  • Among women who experienced menstrual changes after the first dose, almost two out of three women also experienced changes after the second dose.
  • After the second vaccine dose, the proportion reporting menstrual changes was slightly increased for all outcomes.
  • Data about the duration of menstrual disturbances after dose 2 are not yet available, but we continue to monitor this.

"Most menstrual changes after the first dose were transient. On average, they returned to their normal levels by the time of vaccination with the second dose, approximately two to three months after the first dose," explains Trogstad.

Advice for vaccination after menstrual changes

The Norwegian Institute of Public Health gives the following advice to women who have experienced menstrual changes after coronavirus vaccination:

  • Women with persistent menstrual changes should consult their doctor to rule out other diseases that may require treatment.
  • With temporary menstrual changes in a regular cycle, the next vaccine dose can be given as planned.
  • With heavy and persistent bleeding after an earlier dose, it is recommended to delay vaccination until the cause is investigated or the symptoms have passed.
  • For menstrual changes after vaccination that require treatment, the next vaccine dose should be considered on an individual basis, in consultation with a doctor.
  • In cases where women have menstrual changes with another cause than vaccination, they can be given the vaccine against COVID-19.

"If you are in any doubt, consult your doctor," advises Trogstad.

She emphasises that these changes are temporary side effects for the majority and should not prevent women saying yes to a coronavirus vaccine.

"Vaccination gives protection to the individual against a severe COVID-19 course, as well as contributing to reduced transmission in society," she emphasises.

Part of a larger population study

The Norwegian Institute of Public Health is conducting a large study among more than 60,000 women aged 12–80 years in Norway to investigate any association between coronavirus vaccination and different types of menstrual changes. As part of this study, almost 6000 female participants aged 18-30 years in the Norwegian UngVoksen (Young Adult) cohort were asked about their menstrual cycles and bleeding patterns before and after vaccination. The article has been sent in to preprint and is not yet peer-reviewed. The findings should be confirmed by further studies. 

The Norwegian Institute of Public Health is following up with data analyses both in the UngVoksen cohort and in the other cohort studies. Analyses on menstrual changes and other types of bleeding (including postmenopausal bleeding) in other age groups are ongoing and will be available at a later time point.

Further information