Fitting dynamic models to epidemic outbreaks with quantified uncertainty: A primer for parameter uncertainty, identifiability, and forecasts

Chowell, Gerardo

where r represents the intrinsic growth rate in the absence of any limitation to disease spread, K is the size of the epidemic, and a is a parameter that measures the extent of deviation from the S-shaped dynamics of the classical logistic growth model (Turner et al., 1976) . During the early stages of disease propagation when CðtÞ is significantly smaller than K, this model assumes an initial exponential growth phase. To account for initial sub-exponential growth dynamics , we can modify the Richards model replacing the growth term rC by rC p , incorporating a 'deceleration of growth' parameter (p). Hence, the GRM has the form: