Modeling Epidemics: A Primer and Numerus Software Implementation

Wayne M. Getz; Richard Salter; Oliver Muellerklein; Hyun S. Yoon; Krti Tallam

The assumption that pathogen dose can be ignored. The human immune system is extremely complex and takes a variable amount of time to gear up once invaded by a replicating army of pathogens, as the gear-up time depends on the condition of the host, host genetics, and prior host experience with the same and other pathogens. Small pathogen armies (i.e., low doses) are more easily contained by the hosts immune system-that is, before they can replicate to reach levels that may overwhelm and kill the host-than high doses or repeated exposure to lower doses over a short window of time. Such host-immune-system/pathogen dynamics can only be understood using models that are often more complicated than the SEIR model itself [49, 50] . Further, ignoring both single and repeated dose effects may severely compromise the reliability and transferability of SEIR models fitted to one population and then applied to another population or even to the same population at a later date.