A web-based 2 (preexisting position: vaccine-inclined vs. -hesitant) by 2 (message type: scientific evidence vs. misinformation) experimental study was conducted to investigate individuals' processing of misinformation (vis-à-vis scientific evidence) on the vaccine-autism link within the framework of epistemic egocentrism. Data (N = 996) collected with Qualtrics panel demonstrated that preexisting position shaped individuals' responses to vaccine-related messages differently such that vaccine-hesitant individuals processed the message more superficially while vaccine-inclined individuals more systematically. There was evidence that involvement moderated information processing. Vaccine-hesitant and -inclined individuals' intentions to seek further information and to engage others with opposite views in public deliberation were shaped by message perception and source perceptions (trustworthiness and expertise), but in different patterns. Implications of the findings for vaccine-related health communication are discussed.