No(cebo) Vax: COVID-19 Vaccine Beliefs Are Important Determinants of Both Occurrence and Perceived Severity of Common Vaccines' Adverse Effects.

This study highlights the role of psychological influences in triggering and amplifying the adverse effects of the COVID-19 vaccine (i.e., nocebo effects). Fear, beliefs, and expectations about the COVID-19 vaccine, trust in health and scientific institutions, and stable personality traits were measured in 315 adult Italian citizens (145 men) during the 15-min waiting time after vaccination. The occurrence and severity of 10 potential adverse effects were assessed 24 hr later. Nonpharmacological variables predicted nearly 30% of the severity of the vaccine's adverse effects. Expectations are important determinants of adverse effects from vaccines, and the results of the path analyses show that these expectations stem primarily from people's vaccine beliefs and attitudes, which can be changed. Implications for increasing vaccine acceptability and limiting the nocebo effect are discussed.