SPf66 malaria vaccine is a synthetic protein with aminoacid sequences derived from pre-erythrocytic and asexual blood-stage proteins of Plasmodium falciparum. SPf66 was found to have a 31% protective efficacy in an area of intensive malaria transmission in Tanzanian children, 1-5 years old. We report a randomised, double-blind, placebo-controlled trial of SPf66 against clinical P falciparum malaria in Gambian infants. 630 children, aged 6-11 months at time of the first dose, received three doses of SPf66 or injected polio vaccine (IPV). Morbidity was monitored during the following rainy season by means of active and passive case detection. Cross-sectional surveys were carried out at the beginning and at the end of the rainy season. An episode of clinical malaria was defined as fever (> or = 37.5 degrees C) and a parasite density of 6000/microL or more. Analysis of efficacy was done on 547 children (316 SPf66/231 IPV). No differences in mortality or in health centre admissions were found between the two groups of children. 347 clinical episodes of malaria were detected during the three and a half months of surveillance. SPf66 vaccine was associated with a protective efficacy against the first or only clinical episode of 8% (95% CI -18 to 29, p = 0.50) and against the overall incidence of clinical episodes of malaria of 3% (95% CI -24 to 24, p = 0.81). No significant differences in parasite rates or in any other index of malaria were found between the two groups of children. The findings of this study differ from previous reports on SPf66 efficacy from South America and from Tanzania. In The Gambia, protection against clinical attacks of malaria during the rainy season after immunisation in children 6-11 months old at time of the first dose was not achieved.
PIP: During December 1993 to November 1994, in the Upper River Division of The Gambia, 630 infants aged 6-11 months at time of first dose received three doses of malaria vaccine SPf66 or injected polio vaccine (IPV) and were followed up at home during the rainy season using active and passive case detection methods to determine the protective efficacy of SPf66 against clinical episodes of malaria due to Plasmodium falciparum. The researchers were able to use data on only 547 children (316 SPf66/231 IPV) to determine efficacy. The definition of clinical malaria was fever (37.5 degrees Celsius or higher) and a parasite density of at least 6000/mcl. The two groups were essentially the same in terms of mortality, health center admissions, parasite rates, or any other index of malaria. Health workers identified 347 clinical episodes of malaria during the three months of surveillance. SPf66 vaccine had a protective efficacy against first or only clinical episode of malaria of 8% (p = 0.5). Its protective efficacy was 3% against all clinical episodes of malaria. The results of this trial were different than those from earlier reports on SPf66 efficacy from South America and Tanzania. Possible reasons accounting for the different findings were a mistake in coding syringes for the third dose, substantially less intensity of malaria infection in The Gambia than South America, younger children in The Gambia than in Tanzania, genetic differences in the populations, and difference in length of follow-up. In conclusion, protection against malaria during the rainy season after immunization with SPf66 vaccine in infants aged 6-11 months did not occur.