Complexity of the Basic Reproduction Number (R ₀)

Abstract

The basic reproduction number (R ₀), also called the basic reproduction ratio or rate or the basic reproductive rate, is an epidemiologic metric used to describe the contagiousness or transmissibility of infectious agents. R ₀ is affected by numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission and, therefore, is usually estimated with various types of complex mathematical models, which make R ₀ easily misrepresented, misinterpreted, and misapplied. R ₀ is not a biological constant for a pathogen, a rate over time, or a measure of disease severity, and R ₀ cannot be modified through vaccination campaigns. R ₀ is rarely measured directly, and modeled R ₀ values are dependent on model structures and assumptions. Some R ₀ values reported in the scientific literature are likely obsolete. R ₀ must be estimated, reported, and applied with great caution because this basic metric is far from simple.