Quantifying the impact of individual and collective compliance with infection control measures for ethical public health policy

Abstract

Compliance with infectious disease control measures can benefit public health but be burdensome for individuals. This raises ethical questions regarding the value of the public health benefit created by individual and collective compliance. Answering such questions requires estimating the total benefit from an individual’s compliance, and how much of that benefit is experienced by others. This is complicated by “overdetermination” in infectious disease transmission: each susceptible person may have contact with more than one infectious individual, such that preventing one transmission may have no net effect if the same susceptible person is infected later. This article explores mathematical techniques enabling quantification of the impacts of individuals and groups complying with three types of public health measures: quarantine of arrivals, isolation of infected individuals, and vaccination/prophylaxis. The models presented suggest that these interventions all exhibit synergy: each intervention becomes more effective on a per-individual basis as the number complying increases, because overdetermination of outcomes is reduced, Thus additional compliance reduces transmission to a greater degree.