Immunity to falciparum and vivax malaria induced by irradiated sporozoites: a review of the University of Maryland studies, 1971-75.

The immunogenicity in adult male volunteers of sporozoites of Plasmodium falciparum and P. vivax was evaluated at the University of Maryland from 1971 to 1975. Inoculation of large numbers of sporozoites by mosquitos that had been X-irradiated proved safe and well tolerated, and the sporozoites were rendered noninfective. Three volunteers were protectively immunized by this method, one against P. falciparum, one against P. vivax, and one against both species. Protection was species- and stage-specific, but effective against all strains tested within a species, and was reflected by a rise in titre of antibody to the circumsporozoite protein.