People who do not expect anything good from COVID-19 vaccines and have negative experiences with their bodies report worse side effects from the shots, a new study found.

Ten public health researchers published the study Monday in JAMA Network Open, examining 1,678 adults who received a second dose of the Pfizer or Moderna mRNA-based vaccines at a public distribution center in Hamburg, Germany on Aug. 16-28, 2021. From two weeks before vaccination to the next seven days after, participants recorded the symptoms they observed in a daily diary.

The study found participants who expected little to no benefit or significant adverse effects from the shots, who tended to “catastrophize instead of normalize benign bodily sensations” and who had prior negative experiences of the first shot were more likely to report severe aches, pains and other ailments.

According to the researchers, these findings confirm the psychosomatic role of “nocebo effects” in driving vaccine hesitancy.

Nocebo effects occur in medicine when “psychological characteristics including anxiety, depression, and the tendency to amplify benign bodily sensations” lead patients to experience more negative treatment effects than they would otherwise, they wrote.

“Clinician-patient interactions and public vaccine campaigns may both benefit from these insights by optimizing and contextualizing information provided about COVID-19 vaccines,” the researchers said. “Unfavorable nocebo-related adverse effects could then be prevented, and overall vaccine acceptance could be improved.”

Patients who reported more severe tiredness or fatigue, headache, aching limbs, joint pain, chills or fever also tended to misattribute pre-existing symptoms to the vaccines, the study found. It began measuring their symptoms during the two weeks before vaccination.

Overall, 52.1% of participants had high expectations for adverse effects before vaccination. Another 7.6% of participants had a high expectation of being hospitalized over the side effects and 10.6% expected the side effects to be long-term.

While substantial numbers of patients reported adverse effects after vaccination, those with positive expectations reported them as minor. Those who scored higher for anxiety, depression and other psychosocial factors were more likely to flag these issues as severe.

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