S100B and infection: The vaccine regimen consisted of an Adenovirus serotype 5 (Ad5) vector expressing the gag, pol and nef genes of HIV-1 subtype B. The Phambili trial of the same vaccine also entered phase IIb evaluation in South Africa, to explore whether it would also be effective at preventing infection from HIV-1 subtype C. The Step study was stopped due to lack of efficacy and a higher incidence of infections in the vaccinees, followed by a premature halting of the Phambili trial.