FIG. 1.
Structure of the model. Xnp, number of untreated noncolonized individuals; Ynp, number of treated noncolonized individuals; XV,1, XV,2, etc. (or YV,1, YV,2, etc.), numbers of untreated (or treated) individuals colonized by vaccine-type pneumococci with one of the 10 resistance levels (see text); XNV,1, XNV,2, etc., and YNV,1, YNV,2, etc., numbers of individuals colonized by non-vaccine-type pneumococci. The model is structured into three age classes. A portion of children <2 years old are vaccinated, in which case they can be untreated (V) or treated (W); vaccinated children can be colonized only with non-vaccine-type pneumococci.