Safety and immunogenicity of a Plasmodium falciparum sporozoite vaccine: boosting of antibody response in a population with prior natural exposure to malaria

Recombinant sporozoite vaccine or placebo were administered once to 25 volunteers from an area endemic for malaria. Antibody to R32tet32 rose in 9 of 15 receiving vaccine and remained elevated in 6 for 6 months. Mean absorbance increase was 0·43 ± 0·40 with vaccine, 0·01 ± 0·23 with placebo, and 0·72 ± 0·19 in responders. Six non-responders had significantly lower pre-immunization levels (0·07 ± 0·05) than responders (0·39 ± 0·25). There was an association between an increase in immunofluorescence (n = 4) and an increase in absorbence (n = 9) among vaccine recipients (n = 15). Vaccine-induced increase in antibody to natural circumsporozoite antigen was indicated by increases in immunofluorescence and by increases in circumsporozoite precipitation score in 2 of the 5 responders with highest antibody increase measured by enzyme-linked immunosorbent assay. Response to subunit sporozoite vaccine paralleled response to prior natural sporozoite exposure and was significant and prolonged in a population with prior natural exposure to malaria. © 1991.