ANALYSIS OF MULTIPLE PLASMODIUM-FALCIPARUM INFECTIONS IN TANZANIAN CHILDREN DURING THE PHASE-III TRIAL OF THE MALARIA VACCINE SPF66

In the first phase III efficacy trial of the malaria vaccine SPf66 in Africa, MOIs in SPf66- and placebo-vaccinated children were analyzed b y polymerase chain reaction-restriction fragment length polymorphism o f the Plasmodium falciparum merozoite surface antigen 2 (MSA2). MOIs w ere significantly reduced in asymptomatic vaccine recipients compared with those in asymptomatic placebo recipients; however, no differences were observed among symptomatic children in the vaccine and control g roups. These results show that immunization with SPf66 modulates the c ourse of naturally occurring infections, as reflected by reduced MOIs. In placebo recipients, however, there was a significant negative corr elation between numbers of infecting genotypes, as identified by MSA2, and morbidity. Asymptomatic placebo recipients had an average of 5 co ncurrent infections, whereas children with clinical cases had an avera ge of 3.4 infections. These data provide further evidence that premuni tion from concurrent infections is important in immunity against clini cal malaria. No such effect of multiple infections was found in the va ccinated group.