The only HIV vaccine regimen to demonstrate any success—a 31% risk reduction among Thai volunteers a decade ago—has prompted strong immune responses in a new trial in South Africa. Consequently, researchers now think it may not be necessary to tailor HIV vaccines to the predominant strains of the virus in different world regions. The RV144 vaccine regimen uses a “prime-boost” strategy that combines two vaccines based on clades, or subgroups, B and E of the virus. These clades are endemic in Thailand, while clade C is the main HIV strain in South Africa; clade B is predominant in the United States and Europe. In the new study, 52% of the participants developed a CD4 T-cell response to the vaccine, compared with 36% of those in the Thai trial. Both South African and Thai study participants produced antibody responses that crossed viral clades. The antibody responses to clade C antigens, or viral proteins, were higher and more prevalent in the
South African participants.