Epidemiological impact of waning immunization on a vaccinated population

TL;DR

This study uses an SIRV epidemiological model to analyze how waning immunity affects disease dynamics, highlighting differences in vaccination strategies and the conditions leading to endemic states.

Contribution

It introduces a model incorporating waning immunity and analyzes transitions between disease-free and endemic states based on vaccination and conversion rates.

Findings

Vaccination of newborns and adults has different epidemic control effects.

Waning immunity in recovered individuals alone does not trigger epidemics at linear level.

Traveling infection waves can lead to endemic states in diffusive populations.

Abstract

This is an epidemiological SIRV model based study that is designed to analyze the impact of vaccination in containing infection spread, in a 4-tiered population compartment comprised of susceptible, infected, recovered and vaccinated agents. While many models assume a lifelong protection through vaccination, we focus on the impact of waning immunization due to conversion of vaccinated and recovered agents back to susceptible ones. Two asymptotic states exist, the "disease-free equilibrium" and the "endemic equilibrium"; we express the transitions between these states as function of the vaccination and conversion rates using the basic reproduction number as a descriptor. We find that the vaccination of newborns and adults have different consequences in controlling epidemics. We also find that a decaying disease protection within the recovered sub-population is not sufficient to trigger an epidemic at the linear level. Our simulations focus on parameter sets that could model a disease with waning immunization like pertussis. For a diffusively coupled population, a transition to the endemic state can be initiated via the propagation of a traveling infection wave, described successfully within a Fisher-Kolmogorov framework.