Women said covid shots affect periods. A new study shows they're right.

Not long after the rollout of coronavirus vaccines last year, women around the country began posting on social media about what they believed was a strange side effect: changes to their periods.

Now, new research shows that many of the complaints were valid. A study of nearly 20,000 people around the world shows that getting vaccinated against covid can change the timing of the menstrual cycle. Vaccinated people experienced, on average, about a one-day delay in getting their periods, compared with those who hadn't been vaccinated.