Social vs. individual age-dependent costs of imperfect vaccination

In diseases with long-term immunity, vaccination is known to increase the average age at infection as a result of the decrease in the pathogen circulation. This implies that a vaccination campaign can have negative effects when a disease is more costly (financial or health-related costs) for higher ages. This work considers an age-structured population transmission model with imperfect vaccination. We aim to compare the social and individual costs of vaccination, assuming that disease costs are age-dependent, while the disease’s dynamic is age-independent. A model for pathogen deterministic dynamics in a population consisting of juveniles and adults, assumed to be rational agents, is introduced. The parameter region for which vaccination has a positive social impact is fully characterized and the Nash equilibrium of the vaccination game is obtained. Finally, collective strategies designed to promote voluntary vaccination, without compromising social welfare, are discussed. •Highly transmissible diseases with permanent immunity tend to be childhood diseases.•Partial vaccination increases the average age of infection.•Some diseases have a mild effect on children and serious consequences on adults.•Voluntary vaccination with shared costs is considered.•We find conditions such that individual and social interests coincide.