Individual-based perspectives on R0

Without doubt the basic reproductive ratio, R-0, is the most widely used quantity in epidemic theory. Standard compartmental models show how R-0 is related to the average age of infection, vaccination thresholds for eradication and equilibrium solutions. However, many of the basic formulae for R-0 break down when we consider transmission of infection to be a stochastic process involving discrete individuals. This paper clarifies why and when these differences arise and predicts when individual-based considerations are likely to be important in modelling infection dynamics. (C) 2000 Academic Press.