The parasite Plasmodium falciparum causing severe malaria is highly polymorphic. The long time to acquire protective antimalarial immunity may be due to the need to encounter a wide range of parasite variants. Maintenance of such immunity may also depend on persistence of multiclonal infections. We aim to study the genetic diversity and dynamics of P. falciparum infections in childhood in different transmission settings. We investigate potential immunological mechanisms regulating the diversity of infections as well as how new control interventions, e.g. vaccine candidates and intermittent preventive treatment, affect the diversity of infections and protective immunity to malaria. The studies are performed in malaria endemic areas in Kenya, Ghana and Tanzania, as well as in patients diagnosed in Sweden. The research contributes to basic knowledge on protective malaria immunity of importance in the development of an effective malaria vaccine and other control interventions.