For decades, menstrual health has been ignored in clinical trials – especially in vaccine research.
Even as billions of people received vaccines globally, how they might affect menstruation remained an unanswered question.
When COVID-19 vaccinations rolled out worldwide, many women began reporting cycle changes.
But because these were anecdotal, they were often dismissed as coincidence or misinformation.
Minor shifts, major implications
Researchers examined data from over 1,500 women aged 18 to 45 who were not using hormonal birth control.
All participants used a digital fertility tracking app, allowing scientists to compare three cycles before vaccination to the cycle in which they received their shot.
Some women received only the influenza vaccine. Others received both the flu and COVID-19 vaccines at the same time.
In both groups, scientists observed a small but measurable increase in menstrual cycle length – less than one day on average.
Importantly, these changes were temporary. In the cycle after vaccination, most women’s cycles returned to their usual length.
And no statistically significant difference was found between those who received one vaccine versus two.
The timing matter
Women who were vaccinated during the so-called follicular phase – the period before ovulation – experienced a small but noticeable increase in their cycle length.
On average, the cycle length increased by just under one day.
In contrast, there were no changes among women who received the vaccine during the luteal phase, which is the period after ovulation.
However, the changes were temporary. In the cycle following vaccination, everything returned to normal.
Interestingly, a small number of participants experienced more noticeable shifts – up to eight days or more. But this was rare and, again, mostly temporary.
Ultimately, the findings are reassuring. The vaccines don’t cause lasting changes or harm.
But the study fills a crucial gap in knowledge and validates real concerns that have long gone unaddressed.
This article is based on information from Medicalxpress.com.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.