The trial was conducted in more than 16,000 Thailand volunteers. The HVTN 505 trial, which started recruiting participants about a month ago and has enrolled about 30 people thus far, is what Hammer called an "advanced Phase II" trial that will seek to investigate the effects of an HIV vaccine on modulating the viral load in any of the 1350 participants who end up contracting the virus. Like the Thai trial, the HVTN 505 trial uses the "prime-boost" regimen -- where a first round of injections readies the immune system to recognize and combat HIV and a second ramps up immune activity -- but uses a different vector and different vaccine contents.
The vaccine regimen tested in Thailand consisted of priming shots of a canarypox vector carrying three synthetic HIV genes and booster shots of a recombinant form of gp120, a surface protein found in HIV clades B and E. The HVTN 505 study, which is being co-sponsored by the National Institute of Allergy and Infectious Diseases, will administer three priming shots of a recombinant DNA-based vaccine with three HIV genes from clade B followed by booster shots containing the adenovirus serotype 5 (Ad5) vector with HIV viral envelope genes from clades A, B and C.
A principal investigator of the only other ongoing efficacy trial of an HIV vaccine, however, said that “the project needs to be examined more closely to analyze data on subgroup analyses and specific immune responses so that subsequent trials can absorb that information”.
The vice president for vaccine development at the International AIDS Vaccine Initiative, added that the Thai trial is providing promising initial data, 30% efficacy is on the low end of the spectrum regarding the vaccine's potential licensure, explained Hassell. Vaccines typically achieve efficacies of 60-90% before they are officially licensed by the US Food and Drug Administration, he said. This means that the results will spur further research, but the world will have to wait longer for a safe and effective HIV vaccine.
