Coevolutionary vaccination dynamics driven by committed influencers on complex networks.

Voluntary vaccination is often challenged by the vaccination dilemma, wherein individual costs conflict with the collective benefits of herd immunity. Motivated by the considerable influence of online "Big Vs," we introduce a coupled vaccination-epidemic coevolution model on scale-free networks. We incorporate a fraction ρ of committed influencers who consistently advocate for vaccination, incorporating a trust-weighting parameter α to quantify their social influence. Multi-agent simulations and heterogeneous mean-field theory demonstrate that strategic placement of influencers is vital: positioning committed influencers at high-degree nodes results in nearly comprehensive vaccination coverage and substantially suppresses outbreaks across a wide range of vaccination costs. Conversely, random placement proves less effective, and assigning influencers to low-degree nodes necessitates a significantly higher ρ to manage epidemic outbreaks. These results underscore how influence filtered through trust and network heterogeneity can be exploited to develop resilient, resource-efficient vaccination strategies.