Countering vaccine hesitancy through medical expert endorsement.

Scientists and medical experts are among the professionals trusted the most. Are they also the most suitable figures to convince the general public to get vaccinated? In a pre-registered experiment, we tested whether expert endorsement increases the effectiveness of debunking messages about COVID-19 vaccines. We monitored a sample of 2,277 people in Italy through a longitudinal study along the salient phases of the vaccination campaign. Participants received a series of messages endorsed by either medical researchers (experimental group) or by generic others (control). In order to minimise demand effects, we collected participants' responses always at ten days from the last debunking message. Whereas we did not find an increase in vaccination behaviour, we found that participants in the experimental group displayed higher intention to vaccinate, as well as more positive beliefs about the protectiveness of vaccines. The more debunking messages the participants received, the greater the increase in vaccination intention in the experimental group compared to control. This suggests that multiple exposure is critical for the effectiveness of expert-endorsed debunking messages. In addition, these effects are significant regardless of participants' trust toward science. Our results suggest that scientist and medical experts are not simply a generally trustworthy category but also a well suited messenger in contrasting disinformation during vaccination campaigns.