There was a high incidence of the various menstrual changes among menstruating women aged 18-30 years. As many as 37.8 per cent reported at least one of the changes during their last period before vaccination. The proportion who reported heavier periods than normal was higher after the first vaccine dose than before vaccination, 13.6 per cent and 7.6 per cent, respectively.
Results from the first study
- There was a high incidence of the various menstrual changes among menstruating women aged 18–30 years.
- As many as 37.8 per cent reported at least one of the changes during their last period before vaccination.
- The proportion who reported heavier periods than normal was higher after the first vaccine dose than before vaccination, 13.6 per cent and 7.6 per cent, respectively.
- After the second dose, the incidence of various disturbances increased.
- Menstrual changes after the first dose were short-lived and returned to normal by the time for vaccination with the second dose, approximately two to three months after vaccination with the first dose.
- Among women who reported menstrual changes after the first dose, 92.3 per cent were also vaccinated with dose 2. Among women who did not report any disturbances after the first dose, 94 per cent were vaccinated with dose 2.
- Among women who experienced changes after the first dose, almost two out of three women also experienced them after the second dose.
- Data about the duration of menstrual changes after dose 2 are not yet available, but this will continue to be monitored.
These changes were studied among female participants in theUngVoksen cohort study:
- Heavier periods than normal
- Longer bleeding duration than normal
- Shorter interval between periods than normal
- Longer interval between periods than normal
- Unexpected breakthrough bleeding
- More painful periods than normal
- Period-like pains without bleeding
The questions asked were:
- Did you experience any of the following during your last period before the first dose of vaccine?
- Did you experience any of the following during your first period after the first dose of vaccine?
- Did you experience any of the following during your last period before the second dose of vaccine?
- Did you experience any of the following during your first period after the second dose of vaccine?
There was a generally high incidence of the various menstrual disturbances among menstruating women aged 18–30 years: As many as 37.8 per cent reported at least one change during their last period before vaccination. After the first dose, 39.4 per cent reported at least one change, and after the second dose, 40.9 per cent.
In total, 7.6 per cent of participants reported that their last period before vaccination with the first dose was heavier than normal. After vaccination, almost twice as many, 13.6 per cent, reported that the first period after the vaccine was heavier than normal. The same pattern is seen for prolonged bleeding, for shorter intervals between menstrual cycles and for more painful periods than normal, see Table 1.
|Menstrual change||Before 1st vaccine dose (unvaccinated)*||After 1st vaccine dose (vaccinated with at least one dose)*|
|Heavier than normal||7.6%||13.6%|
|Longer duration than normal||9.3%||12.5%|
|Shorter interval between periods||9.5%||12.0%|
|Longer interval between periods||10.3%||10.9%|
|Unexpected breakthrough bleeding||13.8%||14.2%|
|More painful periods than normal||11.4%||14.6%|
|Period-like pains without bleeding||18.3%||15.8%|
*Uncertainty (95% confidence interval was +/- 1% for all menstrual disturbances)
There was no difference before and after vaccination in the incidence of prolonged intervals between menstrual cycles, breakthrough bleeding or period-like pains without bleeding after the first dose. After the second dose, the incidence increased for all the changes, see Table 2.
|Menstrual change||Before 2nd vaccine dose (vaccinated with one dose)*||After 2nd vaccine dose (vaccinated with two doses)*|
|Heavier than normal||8.2%||15.3%|
|Longer duration than normal||8.2%||14.3%|
|Shorter interval between periods||7.9%||14.3%|
|Longer interval between periods||8.4%||10.5%|
|Unexpected breakthrough bleeding||10.0%||15.1%|
|More painful periods than normal||9.8%||16.0%|
|Period-like pains without bleeding||11.8%||16.5%|
*Uncertainty (95% confidence interval was +/- 1% for all menstrual disturbances)
- This is the risk of menstrual changes after the second dose among women who experienced this after the first dose (recurrence risk):
- After vaccination with the first dose of coronavirus vaccine, 13.6 per cent reported unusually heavy periods.
- Among these, almost two out of three women experienced unusually heavy periods after the second dose (65.7 per cent).
- Among women who did not experience heavier periods after the first dose, 8 per cent reported unexpectedly heavy periods after the second dose, which is comparable with the incidence among unvaccinated people.
- For the other menstrual changes, the recurrence risk after the second dose was similar in size.
Vaccination coverage and significance of vaccine type for menstrual changes
Among the participants, 98.4 per cent were vaccinated with the first dose, and 91.8 per cent with two doses. Among these, 59.4 per cent received Comirnaty (Pfizer) as the first dose, 35.8 per cent Spikevax (Moderna), 4.7 per cent AstraZeneca and 0.2 per cent Janssen. For dose two, 47.4 per cent received Comirnaty and 52.6 percent Spikevax. Menstrual changes were reported after both mRNA vaccines, to the same degree.
The responses in the study are based on self-reported data. It is conceivable that women who experienced menstrual changes after the first dose were concerned and thus more likely to report this also after the second dose, compared with women who did not experience menstrual disorders after the first dose. There has been a lot of media attention around the signals that have come after coronavirus vaccination, which may have also contributed to more women reporting menstrual changes after vaccination, even if they have previously experienced similar episodes without vaccination.
Between 50 and 60 of the women had previously had COVID-19. The results did not change because these were excluded from the analyses.
Duration of menstrual changes after vaccination
The study does not provide accurate information about how long the changes persist. However, the results in Table 1 and Table 2 show that the incidence is similar before vaccination with dose 1 and before vaccination with dose 2. For most, the changes were transient and had returned to normal levels when dose two was given, approximately two to three months after vaccination with the first dose. Data about the duration of menstrual disturbances after dose 2 are not yet available, but this will continue to be monitored.
In the analyses among women with menstrual changes, the researchers compared the risk before and after dose 1, and before and after dose 2 in the same women. Since each woman is compared with herself, the analyses also take into account other factors that may have an impact, such as contraception, use of other medications, or other gynaecological complaints or diseases.
In this analysis, there was a nearly doubled risk (90 per cent increase) of experiencing heavier periods than usual after vaccination with the first dose, relative risk (RR) 1.90 (95 per cent confidence interval 1.69-2.13). After the second dose the relative risk was 1.84 (95 per cent confidence interval 1.66-2.03). An increased risk after the second dose is also seen for prolonged bleeding, shorter intervals between periods, longer intervals between periods, unexpected breakthrough bleeding, more painful periods, and period-like pains without bleeding than usual, see Table 3.
|Menstrual change||Relative risk and 95% confidence interval after 1st vaccine dose||Relative risk and 95% confidence interval after 2nd vaccine dose|
|Heavier than normal (634 dose 1, 557 dose 2)||1.90 (1.69-2.13)||1.84 (1.66-2.03)|
|Longer duration than normal (636 dose 1, 541 dose 2)||1.46 (1.31-1.61)||1.71 (1.55-1.89)|
|Shorter interval between periods (603 dose 1, 488 dose 2)||1.32 (1.19-1.46)||1.57 (1.42-1.73)|
|Longer interval between periods (594 dose 1, 434 dose 2)||1.07(0.97-1.17)||1.24 (1.13-1.37)|
|Unexpected breakthrough bleeding (725 dose 1, 559 dose 2)||1.09 (1.01-1.17)||1.49 (1.37-1.62)|
|More painful periods than normal (706 dose 1, 582 dose 2)||1.35 (1.24-1.47)||1.62 (1.49-1.77)|
|Period-like pains without bleeding (830 dose 1, 583 dose 2)||0.91 (0.86-0.97)||1.36 (1.27-1.45)|
The results are based on questions answered by almost 6,000 female participants in the Norwegian UngVoksen (Young Adult) cohort in the period 21 October to 11 November 2021. The study has not yet been peer-reviewed but has been submitted for preprint. The findings should be confirmed by other studies.
Follow-up and data analyses continue in both UngVoksen and in the other cohort studies. These will provide answers about menstrual changes and bleeding in other age groups, and the duration of the symptoms.
Menstrual changes are common
Menstrual changes are very common among women of childbearing age and can have various causes. Menstruation can be affected by many factors, such as infections, medicines, hormones / contraception, fibroids, endometriosis or other diseases of the uterus and cervix. When many women are vaccinated, it is therefore expected that some will experience menstrual changes and unexpected bleeding around the time of vaccination by coincidence.
Early in summer 2021, initial reports came that more women were experiencing menstrual changes that they associated with vaccination. To investigate whether there is a connection between coronavirus vaccination and menstrual changes, the Norwegian Institute of Public Health is conducting a large study among more than 60,000 women aged 12–80 in Norway. Through online questionnaires, participants answer questions about their periods and any menstrual changes.
The main purpose of the study is to find out whether these changes occur more frequently among vaccinated than non-vaccinated women.
Throughout the pandemic, participants in Norwegian population studies have regularly answered questions about health problems and diseases, COVID-19 disease, quarantine, testing, vaccination and symptoms or side effects after vaccination.
The contribution from the participants is invaluable and provides unique knowledge about conditions that is not available from national health registries. We are extremely grateful for the efforts and perseverance shown by the participants throughout the pandemic.
Data from the population studies have previously been used in a study where an increased risk of skin haemorrhaging was identified after vaccination with Vaxzevria (AstraZeneca) compared with Comirnaty (Pfizer / BioNTech) or Spikevax (Moderna). The results of this study are published in the journal Vaccine.
- Trogstad L et al. Association between ChAdOx1 nCoV-19 vaccination and bleeding episodes: Large population-based cohort study. Vaccine. 2021 Sep 24;39(40):5854-5857. doi: 10.1016/j.vaccine.2021.08.055 https://www.sciencedirect.com/journal/vaccine/vol/39/issue/40