Apple study finds COVID-19 jabs may lengthen menstrual cycle

by Jonny Evans · Published November 3, 2022 · Updated November 3, 2022

Apple’s ongoing Women’s Health Study has identified that COVID-19 vaccines do extent the menstrual cycle slightly, but the impact is only temporary.

Only a slight impact and only for a short time

The study includes over 9,600 subjects who logged over 128,000 cycles, which is a substantial sample group. 88% of the group were vaccinated and the study suggests the cycle then extends by 0.5 days on the first dose and 0.39 days on the second.

The study, as reported by npj Digital Medicine (via MobiHealth News) also found that the single dose Johnson and Johnson vaccine extends cycles by 1.26 days. This effect lasts only for one or two cycles.

The study also determined that it makes a difference when in the cycle a woman takes the vaccine – doing so during the follicular phase (when the egg is about to be released) tends to extend the cycle for some reason.

“Our results suggest a small, non-persistent increase in average length of menstrual cycles in which a vaccine was administered. Moreover, the J&J vaccine was associated with a significant increase in the probability of a clinically long (>38 days) cycle; however, this increase did not persist over time,” the authors said.

“We found evidence that vaccination increased cycle length for approximately 1–2 cycles post-vaccination. After this, cycles returned to their pre-vaccination mean.”

Toward more gender equality

Apple’s study is an important piece of work. In 2021 it published statistical research based validation of women’s experiences of a wide range of menstrual cycle symptoms including some that are less commonly known or discussed.

“Our study will help to achieve a more gender equal future, in which all people with menstrual cycles have access to the health services and menstrual products needed to feel safe and empowered,” said Dr. Michelle Williams, Dean of the Faculty at Harvard Chan School at that time.

U.S. women can take part in the Apple Women’s Health Study. iPhone and Apple Watch users across the US should first download the Research app.

📱 Sumbul Desai, @Apple's VP of health, joined us on Centre Stage this afternoon to deliver a keynote address on creating technology that empowers people to lead healthier lives ❤️ pic.twitter.com/WNZm16Q174

— Web Summit (@WebSummit) November 3, 2022