LONG-TERM PERSISTENCE OF STERILE IMMUNITY IN A VOLUNTEER IMMUNIZED WITH X-IRRADIATED PLASMODIUM-FALCIPARUM SPOROZOITES

Three volunteers were immunized by repeated exposure to the bites of P lasmodium falciparum-infected, X-irradiated mosquitoes to characterize immunologic responses and duration of protective immunity. A primary series of immunizations had been shown previously to induce sterile im munity in these volunteers against sporozoite-induced P. falciparum ma laria. In the current study, antibodies to sporozoites circulated at h igh levels for at least 9-12 months after the volunteers were administ ered booster bites from X-irradiated infective mosquitoes. One volunte er challenged a second time with P. falciparum 9 months after his last immunization was again shown to be protected, whereas all 5 control s ubjects developed patent infections. These results set a new standard for persistence of sterile immunity against experimental P. falciparum infection.