A phase I safety and immunogenicity trial with the candidate malaria vaccine RTS,S/SBAS2 in semi-immune adults in the Gambia

RTS,S is a novel pre-erythrocytic malaria vaccine based on the circumsporoz oite surface protein (CSP) of Plasmodium falciparum linked to hepatitis B s urface antigen (HBs) and combined with a novel adjuvant system (SBAS2). We have conducted a Phase I trial with three doses of this vaccine given at 0, 1, and 6 months to 20 semi-immune, adult, male volunteers in The Gambia to assess its safety and immunogenicity. Eighteen of the 20 volunteers comple ted the study. There were no clinically significant local or systemic adver se events following each vaccination. Hematologic and biochemical indices b efore and two weeks after each vaccination showed no evidence of toxicity. Antibody titers to both CSP and HBs showed a significant increase after vac cination; these were the largest after the third dose. We conclude that the RTS,S/SBAS2 vaccine induces no significant toxicity in this semi-immune po pulation and produces significant increases in antibody titers to CSP.