'Nocebo' effect may account for 76% of COVID-19 vaccine side effects

When placebos elicit adverse events, these are often called nocebo responses. A study finds that a third of people who received placebos during COVID-19 vaccine clinical trials reported unpleasant systemic side effects such as headache and fatigue. The authors of the study find that 76% of side effects reported by actual vaccine recipients are likely the same effects and attributable to nocebo responses.