Social \textit{vs.} individual age-dependent costs of imperfect vaccination

TL;DR

This paper analyzes how imperfect vaccination affects age-dependent disease costs in an age-structured population, highlighting the social and individual impacts and identifying conditions for positive vaccination strategies.

Contribution

It introduces an age-structured model comparing social and individual vaccination costs, and characterizes the conditions for beneficial vaccination policies and equilibrium strategies.

Findings

Vaccination can have negative effects if disease costs increase with age.

The model identifies parameter regions where vaccination benefits society.

Strategies for promoting voluntary vaccination without social welfare loss are discussed.

Abstract

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 coupling pathogen deterministic dynamics for 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.