“We need to remember to ask about differences in the menstrual cycle as part of standard clinical testing of vaccines. We know that there will be a huge immune response, which can disrupt lots of inflammatory pathways, and menstrual cycles are something women who have periods will pay attention to.” Dr. Katharine Lee
COVID-19 and the menstrual cycle
Previous research has shown that viral infections can impact the menstrual cycle. And COVID-19 is no different - menstrual cycle changes have been reported following infection. Studies looking into menstrual cycle change during the pandemic have also noted increased cases of menstrual disturbance compared to pre-pandemic.
A study examining self-reported symptoms of long COVID found high levels of menstrual disruption, with over 1/3 of respondents reporting new menstrual cycle issues.
Unusual clotting of period blood
More severe long COVID symptoms around the time of their periods
It remains unclear whether reported changes are due to COVID-19 itself or other pandemic-related factors (such as psychological stress or behaviour change).
Vaccines and the menstrual cycle
A range of menstrual cycle disorders have been reported after all three of the UK approved COVID-19 vaccines. The Times received 4,000 reports of changes to people’s menstrual cycles after vaccination by May 17, 2021. 69% of these women had the Oxford-AstraZeneca, 29% Pfizer, and 2% Moderna.
The main side effects:
For those that regularly bleed - heavier, longer, or delayed periods
For those that don’t - cramps or spotting
These changes seem to be common in the immediate cycle post vaccination, with subsequent cycles returning to baseline. Most women don’t experience any changes.
Remember: There is no impact on fertility or pregnancy from the vaccine.
Since we don’t have systematic data on COVID-19 vaccines’ effects on the menstrual cycle (the trials neglected to ask about menstrual cycle impact), we can’t be certain that any reported differences are a direct result of the vaccine. However, in the absence of enough data we have to listen to people’s voices and lived experiences.
What might explain these menstrual cycle changes?
Our uterine lining is part of the immune system - when we get a vaccine our immune system responds. The compounds and cells involved in this immune function are also involved in menstruation - cue changes occurring.
Stress of a vaccine could affect hormone production and menstruation - stress can alter the brain regions responsible for kick-starting reproductive hormone production. If stress is the culprit it means the potential link between vaccination and menstruation isn't a direct one.
More aware of changes - people might be paying more attention to their bodies after getting a vaccine because they may be anticipating side effects. Any changes in how they feel or physical things they experience could be attributed to the vaccine when in reality they might be completely unrelated.
Note: other vaccines (such as HPV) have been linked to short-term changes in menstrual cycles.
Who seems to be more impacted
Anyone with a prior disorder that affects bleeding or clotting.
Those who have had more endometrial practice - older people who have had more menstrual cycles, those who have been pregnant or given birth. Their vasculature of the uterus is more established so may experience heavier bleeding after a vaccine.
Those who have higher levels of oestrogen; more common in women over 40 as they need increased signal from the brain to stimulate ovulation.
What to do if you do experience a change
If you already track your menstrual cycle and symptoms, continue doing so to spot for changes around your vaccine or if you have COVID-19.
For any missed periods, always check with a pregnancy test.
If experiencing pain or significant persistent changes check in with your doctor.
Any women experiencing bleeding after menopause seek medical advice.
The benefits outweigh the potential risks
The COVID-19 vaccine is arguably the world's most important tool in the fight against the pandemic. Getting COVID-19 has far worse impacts on long-term health, for future fertility, or for your period than getting the vaccine.
We need to keep pushing for menstruating people to be included in clinical trials, recording any period-related effects, and keeping the public informed of what changes they can expect.