A pilot safety and immunogenicity trial of the malaria vaccine SPf66 was undertaken in The Gambia in 1993. One hundred and fifty infants aged 6-11 months were immunized with either 0.5 mg or 1.0 mg of SPf66 produced either in Colombia or in the USA or with a control vaccine. Children who received SPf66 experienced more clinical attacks of malaria than did children in the control group during the first period of surveillance and the difference in incidence between children who had received high dose Colombian vaccine and the control children was statistically significant at the 5% level. During the 1995 malaria transmission season, 127 children from the original cohort of 150 were observed. During 18 weeks of intensive surveillance, the incidence of clinical malaria was again higher among children who had received SPf66 than among children who had received inactivated polio vaccine (6.23 vs 4.89 clinical attacks per 1000 days at risk), the effect being most marked among children who were in the high dose groups, but differences between groups were now no longer statistically significant.
PIP: 150 human subjects aged 6-11 months were involved in a pilot safety and immunogenicity trial of the malaria vaccine SPf66 conducted in The Gambia in 1993. The infants were immunized with either 0.5 mg or 1.0 mg of the vaccine produced in either Colombia or the US, or with a control vaccine. Children who received SPf66 experienced more clinical attacks of malaria than did children in the control group during the first period of surveillance, with the difference in incidence between children who had received high dose Colombian vaccine and the control children being statistically significant. 127 children from the original cohort of 150 were observed during the 1995 malaria transmission season. During 18 weeks of intensive surveillance, the incidence of clinical malaria was again higher among children who had received SPf66 than among children who had received inactivated polio vaccine. The effect was most marked among children in the high dose groups, although the intergroup differences were statistically insignificant. The SPf66 vaccine may have induced an immune response which made the immunized children more susceptible to malaria. It is also possible that the increased susceptibility to malaria among children who received SPf66 was a chance event following the randomization process. No enhancement of either disease frequency or severity was found in a much larger efficacy trial of Colombian SPf66 conducted among Gambian children during a 2-year follow-up period.