A test of vaccine endorsement by political in- versus out-group sources: Effect on vaccination likelihood and exploration of mediation through perceived bias and liking

This study investigated whether political endorsements from in- versus out-group political elites would influence likelihood of COVID-19 vaccination. In March 2021, we ran an experiment with Democrats and Republicans in the United States to examine whether they would be more likely to get vaccinated following endorsements by former Presidents Obama or Trump. Participants reported greater likelihood of getting vaccinated if the vaccine was endorsed by an elite from their own rather than the opposing party. This effect was driven by Trump, who increased vaccination likelihood among Republicans but decreased it among Democrats. We also investigated the mechanisms underlying this persuasion effect and found that perceived bias and liking were plausible mediators, whereas perceived trustworthiness and expertise were not. This study highlights the potential of having endorsements from both Democrat and Republican political elites to increase support for health behaviors in a politically charged climate.