Impact of disease risk on the narrative bias in vaccination risk perceptions

Objective: Previous studies have shown that even when a statistical base-rate of vaccine adverse events (VAE) is provided, a small sample of single-case narratives influences vaccination risk perceptions and vaccination intentions, irrespective of various content characteristics. This study investigated whether this narrative bias is moderated by an environmental feature, namely the risk of the disease.Design: In three online-experiments, 564 subjects were presented with statistical information (20%) about the probability of VAE associated with a hypothetical vaccination and with a sample of narratives describing personal vaccination experiences. The relative frequency of narratives reporting VAE was varied between-subjects (5/20/35%) to test for a bias. Three potential moderators were tested: likelihood of infection, severity of disease and perceived susceptibility to the disease.Main outcome measures: Perceived risk of vaccination and intention to get vaccinated.Results: Compared to the control condition (20%), narratives reporting VAE increased (35%) and decreased (5%) risk perceptions, which affected vaccination intentions respectively. This bias was not affected by any variable pertaining to the disease risk.Conclusion: People's vaccination decisions are reliably affected by small samples of single-case vaccination experiences. As this influence works in either direction, health communicators should provide people with many examples of safely completed vaccinations.