We extend our basic discrete-event model of Plasmodium falciparum malaria to encompass circumstances in which multiple phenotypic variants of the parasite circulate within interacting human and mosquito populations, and we compare a version in which variants behave independently to one in which they interact through shared host immune responses. Relative to the standard hypothesis of statistical independence, frequencies of mixed-phenotype infection in humans were as expected in the independent-immunity version and much less than expected in the cross-immunity version; in both versions, however, such frequencies in mosquitoes were much greater than expected.