Figure 2

Steady state infection level. The proportion of people with P. falciparum infections increases extremely rapidly as vectorial capacity increases, but there is a large shift between those who are nonimmune and those who are immune. Semi-immune individuals mirror the trajectory of total infections as vectorial capacity increases and quickly become the large majority of infections. At low levels of vectorial capacity, the proportion of the population that is clinically immune remains extremely low. However, as vectorial capacity increases, the proportion of individuals that are clinically immune (nonimmune) increases (falls). The clinical incidence rate increases sharply at first but then plateaus as the proportion of the population that is clinically immune increases. The clinical incidence rate is defined at equilibrium as the sum of susceptible individuals who become infected with a wild-type phenotype and develop an immediate clinical infection plus individuals already infected who become symptomatic $\left({\displaystyle \sum _i{\displaystyle \sum _j{h}_w{S}_j{\xi }_j+I_{i,j}{s}_j}}\right)$, where i and j are the phenotype of the infection and the immune stage, respectively.