An Individual-Based Model In Maintaining Herd Immunity: Case On Malaysia Pertussis Data

Public health controls the re-emergence of infectious diseases by achieving herd immunity establishment in the population. This paper aims to consolidate two factors affecting herd immunity namely individuals' trust in public health and vaccines as well as wane of immunity in individuals into one epidemiological model in maintaining herd immunity. The model formulation adopts Individual-Based Model (IBM) approach to address the heterogeneity effects of individuals' attributes. The individuals' vaccination decision is modelled with imitation dynamics based on game theory. The model simulations use the real parameters obtained for Pertussis in Malaysia. By using different probability of individuals acquire trust, the simulation results are validated with the real Pertussis prevalence where the Root-Mean-Square-Percentage-Error (RMSPE) is used as the accuracy measurement metric. Around 70 percent to 80 percent of individuals must acquire trust towards public health and vaccines so that the simulation results become more fitted to the real Pertussis prevalence. In addition, the modified herd immunity threshold formula is derived from the model and is analyzed through parameter sensitivity analysis. Comparing to the general formula of herd immunity threshold, the modified herd immunity threshold formula provides a higher threshold for the establishment of herd immunity due to additional parameters included in the formula. The disruption of herd immunity because of the wane of immunity in individual would be countered by the vaccination of individuals who trust in public health and vaccines, hence establishing the herd immunity in the population. (Abstract)