SAFETY, IMMUNOGENICITY AND PROTECTIVE EFFECT OF THE SPF66 MALARIA SYNTHETIC VACCINE AGAINST PLASMODIUM-FALCIPARUM INFECTION IN A RANDOMIZEDDOUBLE-BLIND PLACEBO-CONTROLLED FIELD TRIAL IN AN ENDEMIC AREA OF ECUADOR

A total of 537 subjects were randomized to receive either SPf66 malari a vaccine against Plasmodium falciparum or placebo in three doses (day s 0, 30 and 180). Subjects completing the course of vaccination (230 i n the vaccine and 238 in the placebo group) were followed up for a fur ther 12 months. Case detection surveillance was implemented by parasit ological cross-sectional surveys every 2 months and by monthly househo ld visits to each participant. Symptomatic subjects were also diagnose d in a local health centre. Minor local side-effects were observed mai nly after the second dose in about 19% of the vaccinated subjects and in 3.7% of the placebo group. Thirty days after the third dose the pre valence of anti-SPf66 antibodies was 57% in the vaccine and 8.8% in th e placebo groups. The prevaccination prevalence of antibodies measured by indirect immunofluorescence assay increased with age and seemed to be inversely related to anti-SPf66 antibody production. Immune respon se to SPf66 was independent of age. Vaccine efficacy was calculated ba sed on person-time of exposure. The protective effect considering any malaria episode was 66.8% (95% confidence interval=-2.7-89.3%) and con sidering only one episode per individual was 60.2% (95% confidence int erval=-26-87.5%).