Many continue to worry about experiencing side effects from vaccines — especially the COVID-19 vaccines — but new data from a comprehensive meta-analysis suggests there is little to fear. The study from Beth Isreal Deaconess Medical Center found that a large number of side effects reported by patients after receiving their shot can be attributed to the placebo effect.

Researchers examined 12 vaccine safety trials, involving thousands of people, and compared rates of side effects reported between those who received a placebo shot and those who received a real shot. They found that after the first shot, two-thirds of people experienced side effects like headache and fatigue, which the researchers said were attributable to the placebo effect. Shockingly, nearly a quarter of the people — some who received the placebo shot — experienced side effects like a sore arm, also attributable to the placebo effect.

After the injection, people are more aware now that they think they might have gotten a vaccine. They’re more likely to tell their doctor about things,” Schaffner said. “Never underestimate the power of the human mind.”