Abstract
BACKGROUND: Doubts regarding vaccine effectiveness may prompt people to decide against a seasonal influenza vaccination. While fact boxes show the effectiveness in terms of cases prevented, people often lack knowledge about important contextual factors, for example, why the vaccine formulation needs to be updated annually, the vaccine mechanism and relevance of the antigen-virus match. Adding such contextual information could improve effectiveness perceptions. OBJECTIVE: In a preregistered online experiment, we tested whether explaining the seasonality's relevance and mechanisms behind influenza vaccine effectiveness affects people's perceptions of influenza vaccination. We compared two means of explanation (an additional expository text vs. a narrative offering an analogy to improve understanding of vaccine effectiveness) with a control condition simply providing effectiveness information. DESIGN: Unvaccinated participants (N = 1554) were assigned to one of three conditions: (1) fact box only (providing the influenza vaccine's benefit-risk profile; control group), (2) fact box plus informational expository text or (3) fact box plus narrative analogy. METHODS: After the experimental manipulations, participants rated the vaccine's effectiveness in preventing influenza disease and answered knowledge questions. Effects on perceived risk of vaccination and intention to get vaccinated were also explored. RESULTS: Reading the expository text increased the perceived vaccine effectiveness and overall knowledge, while reading the narrative analogy only increased the perceived vaccine effectiveness compared with the control condition. All other dependent variables were similar in both text conditions. CONCLUSIONS: Extended explanations of vaccine effectiveness can increase perceived vaccine effectiveness. The text format chosen can affect outcomes, such as vaccine-related perceptions or knowledge.