After Katherine Lee received her COVID-19 vaccine, she and a colleague chatted about their side effects. Because they worked in a medical school, they received their shots early and felt this might be a good opportunity to understand the experience. While they expected injection site pain and to maybe spike a fever, they both noticed a symptom that they had not expected: their menstrual cycles changed. As Lee began talking with other people who menstruated, she heard that they also experienced periods that came earlier, felt heavier or just seemed abnormal. To read the full story.