One side effect of the COVID-19 vaccine could be a heavier period

Katharine Lee got her COVID-19 vaccination early on in the United States‘ rollout. So did a friend of hers — they got their shots on the same day. They compared notes, curious to see what the side effects would be. Lee, a research fellow in the Division of Public Health Sciences at Washington University in St. Louis, says that they both had one surprising symptom: they both started their period soon after they took the vaccine.