Basic reproductive rate

Definition

In epidemiology and population biology, the expected number of new infections or individuals produced by a single infected or reproducing individual introduced into a completely susceptible population, in the absence of immunity, prior infection, or control interventions. Denoted R₀ or R₀, this dimensionless threshold parameter determines whether a pathogen or population will invade (R₀ > 1) or fail to establish (R₀ < 1). Despite its name, it is a ratio, not a rate with time units.

Etymology

Example

In malaria control, reducing the basic reproductive rate of Plasmodium falciparum below 1 through insecticide-treated bed nets that kill Anopheles vectors can lead to local elimination, even when human prevalence remains high.

Synonyms

• basic reproduction number
• R₀
• R-naught

Related Terms

• effective reproductive rate
• vectorial capacity
• force of infection
• herd immunity threshold
• generation time
• reproductive number

Usage Notes

Distinguished from the effective reproductive rate (R or Rₜ), which reflects transmission under current conditions including immunity and interventions. In arthropod-borne disease systems, R₀ incorporates vector parameters: mosquito density, biting rate, vector competence, and vector mortality. Some ecologists reserve 'reproductive rate' for per-capita offspring production and use 'reproduction number' for epidemiological contexts, though the terms are often conflated.