Efficacy of recombinant circumsporozoite protein vaccine regimens against experimental Plasmodium falciparum malaria

After initial successful evaluation of the circumsporozoite-based vaccine R TS,S/SBAS2, developed by SmithKline Beecham Biologicals with the Walter Ree d Army Institute of Research, protective efficacy of several regimens again st Plasmodium falciparum challenge was determined. A controlled phase 1/2a study evaluated 1 or 2 standard doses of RTS, S/SBAS2 in 2 groups whose mem bers received open-label therapy and 3 immunizations in blinded groups who received standard, one-half, or one-fifth doses. RTS, S/SBAS2 was safe and immunogenic in all groups. Of the 41 vaccinees and 23 control subjects who underwent sporozoite challenge, malaria developed in 7 of 10 who received 1 dose, in 7 of 14 who received 2 doses, in 3 of 6 who received 3 standard d oses, in 3 of 7 who received 3 one-half doses, in 3 of 4 who received 3 one -fifth doses, and in 22 of 23 control subjects. Overall protective efficacy of RTS, S/SBAS2 was 41% (95% confidence interval, 22%-56%; P = .0006). Thi s and previous studies have shown that 2 or 3 doses of RTS, S/SBAS2 protect against challenge with P. falciparum sporozoites.