Do Celebrity Endorsements Matter? A Twitter Experiment Promoting Vaccination in Indonesia.

This article examines the impact of celebrity endorsements on public health messaging through a large-scale Twitter experiment conducted in Indonesia from 2015 to 2016, focusing on promoting immunisation. The study finds that tweets authored directly by celebrities are 72% more likely to be liked or retweeted than similar messages without visible celebrity authorship, with 66%–76% of this effect attributable to celebrities speaking in their own voice rather than merely relaying others' messages. Contrary to expectations, including citations of public health authorities in tweets reduces message diffusion by about 27%. Phone surveys indicate that exposure to celebrity-endorsed messages correlates with increased offline awareness, improved knowledge about vaccine origins, greater communication about immunisation among neighbors, and higher reported immunisation rates within social networks, though no significant change was found in individuals' own immunisation behavior. These findings suggest that celebrity-authored messaging can effectively enhance the spread and offline impact of public health campaigns, emphasizing the importance of authentic celebrity involvement over sourced or relayed content.