Forming and updating vaccination beliefs: does the continued effect of misinformation depend on what we think we know?

People may cling to false facts even in the face of updated and correct information. The present study confronted misconceptions about the measles, mumps and rubella vaccine and a novel, fictitious Zika vaccine. Two experiments are reported, examining misconceptions as motivated by a poor risk understanding (Experiment 1, N = 130) or the exposure to conspiracy theories (Experiment 2, N = 130). Each experiment featured a Misinformation condition, wherein participants were presented with fictitious stories containing some misinformation (Experiment 1) and rumours focused on conspiracy theories (Experiment 2) that were later retracted by public health experts and a No misinformation condition, containing no reference to misinformation and rumours. Across experiments, participants were more hesitant towards vaccines when exposed to stories including vaccine misinformation. Notwithstanding, our results suggest a positive impact of a trusted source communicating the scientific consensus about vaccines. Zika virus represents a particular case showing how missing information can easily evolve into misinformation. Implications for effective dissemination of information are discussed.