Using the Diffusion of Innovation Theory to Understand COVID-19 Booster Hesitancy in Adults

COVID-19 vaccine hesitancy is well documented, but less is known about booster hesitancy among fully vaccinated adults. A qualitative approach was employed to identify factors affecting COVID-19 booster hesitancy using diffusion of innovation (DoI) theory. The study was conducted in Philadelphia, Pennsylvania. In-depth interviews (n = 30) were done with adults, including those who had (n = 9) and had not (n = 21) been boosted. Participants were categorized into DoI adopter groups or a "refuser" group for those with no intention of getting boosted. Transcripts were analyzed using an iterative coding process with consensus and triangulation to develop thematic categories. Participants had a mean age of 41 and were 63.3% Black; 20% were classified as innovators, 6.7% early adopters, 3.3% early majority, 6.7% late majority, 43.3% laggards and 20% refusers. Three themes varied across groups: level of perceived risk susceptibility of getting COVID-19 in the future, information needs and levels of vaccine literacy, and effects of ongoing institutional mistrust. Those in the laggard and refuser groups generally had lower vaccine literacy, higher levels of institutional mistrust, and were more likely to listen to friends and family for booster advice, all consistent with DoI adopter characteristics. These differences indicate important intervention targets to promote booster uptake, especially in those who have been previously vaccinated.