Covid-19 vaccination confirmed to have effect on period


The production of inflammatory proteins known as cytokines triggered by the Covid-19 vaccine disrupts the way the body regulates the menstrual cycle. — AFP

Women vaccinated against Covid-19 saw a slight delay in their period of almost a day compared to those who were unvaccinated, a US government-funded study said on Jan 13 (2021).

But the number of days of bleeding was not affected, according to the research carried out on nearly 4,000 individuals and published in the journal Obstetrics & Gynecology.

Lead author Dr Alison Edelman of the Oregon Health & Science University in the United States said that the effects are small and expected to be temporary – a finding that is “very reassuring”, as well as validating for those who experienced changes to their menses.

The study can also help counter anti-vaccine misinformation on the topic, which is rampant on social media.

The slight increase in menstrual cycle length is not clinically significant.

Any change of fewer than eight days is classified as normal by the International Federation of Gynecology and Obstetrics.

Period cycles generally last about 28 days, but the precise amount varies from one woman to another, as well as within an individual’s lifetime.

It can also change during times of stress.

For their study, the scientists analysed anonymised data of women aged 18 to 45, who were not using hormonal contraception, from a fertility-tracking app.

Some 2,400 participants were vaccinated – the majority with the vaccine from Pfizer-BioNTech (55%), followed by Moderna (35%) and Johnson & Johnson (7%).

About 1,500 unvaccinated women were also included as a comparison.

Among the vaccinated group, data was collected from three consecutive cycles before vaccination and from three more consecutive cycles, including the cycle or cycles in which vaccination took place.

For unvaccinated individuals, data was collected for six consecutive cycles.

On average, the first vaccine dose was associated with a 0.64-day in- crease in cycle length and the second dose with a 0.79-day increase, when comparing the vaccinated to unvaccinated group.

The immune system’s response to the vaccine could be behind the change.

“We know that the immune system and the reproductive system are interlinked,” said Dr Edelman.

A revved-up immune system might have an impact on the hypothalamic-pituitary-ovarian axis – what she calls the “highway of how your brain talks to your ovaries, talks to your uterus”, or also known as the “body clock”.

Specifically, the production of inflammatory proteins called cytokines appears to disrupt the way this axis regulates the timing of menstrual cycles.

The changes seem most pronounced when vaccination takes place early in the follicular phase, which starts on the first day of the menstrual period (i.e. bleeding) and ends when ovulation begins.

In fact, a subgroup of people who received two injections of the Pfizer-BioNTech or Moderna vaccines during the same cycle, as opposed to two different cycles, saw an average increase in cycle length of two days, but the effect again appears temporary.

The team now hopes to gather more data on subsequent cycles among vaccinated women to confirm a long-term return to baseline, and expand the study globally so that they can differentiate the effects between different Covid-19 vaccine brands. – AFP Relaxnews

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