A Phase IIb Randomized, Double-blind, Controlled Study of the Safety, Immunogenicity and Proof-of-concept of RTS,S/AS02A, and RTS,S/AS01B, Two Candidate Malaria Vaccines in Malaria-experienced Adults Living in Western Kenya.

The candidate malaria vaccine RTS,S/AS02A developed by GSK Biologicals demonstrated 30% efficacy against clinical episodes of malaria and approximately 58% efficacy against severe malaria disease. As a potential improvement to RTS,S/AS02A, another candidate vaccine RTS,S/AS01B is being developed in parallel in collaboration with the Walter Reed Army Institute of Research (WRAIR). This study will be the first administration of the RTS,S/AS01B vaccine to the African adults to establish safety and immunogenicity in this population. Preliminary indication of vaccine efficacy with this adjuvant will be established by monitoring the time to the first infection with Plasmodium falciparum.