RANDOMIZED DOUBLE-BLIND PLACEBO-CONTROLLED TRIAL OF SPF66 MALARIA VACCINE IN CHILDREN IN NORTHWESTERN THAILAND

Background Previous efficacy trials of SPf66 malaria vaccine have prod uced conflicting results in different populations. We report a randomi sed double-blind trial of the SPf66 vaccine conducted in Karen childre n aged 2-15 living in a malarious region of northwestern Thailand. Rec ombinant hepatitis B vaccine was used as a comparator. Methods The stu dy had a power of 90% to detect an efficacy of 30%, defined as a reduc tion in the incidence of first cases of symptomatic falciparum malaria after three doses of vaccine. 1221 children received three immunisati ons acid were eligible for the primary efficacy analysis. Intense acti ve and passive case detection continued over 15 months of follow-up. F indings The SPf66 vaccine was well tolerated, although 26 children had mild or moderately severe local or systemic allergic reactions, compa red with none in the comparator group. The vaccine was immunogenic; af ter three doses, 73% of recipients had seroconverted. There were no de aths due to malaria during the study. During the 15-month period of ev aluation there were 379 first cases of symptomatic falciparum malaria (195 in the SPf66 recipients, 184 in the comparator group); an SPf66 e fficacy of -9% (95% CI -33 to 14, p=0.41). No significant differences between the two study groups in parasite density or any other measure of malaria-related morbidity were detected. Interpretation These findi ngs are consistent with a recent study showing lack of efficacy of SPf 66 among Gambian infants and differ from earlier positive reports from South America and evidence of borderline efficacy from Tanzania. We c onclude that SPf66 does not protect against clinical falciparum malari a and that further efficacy trials are not warranted.