The Quest for an HIV Vaccine
The HIV vaccine field received exciting news Thursday from an HIV vaccine trial conducted in Thailand, where the vaccines tested appeared to reduce the acquisition of HIV by about 30 percent. This milestone is the first sign from a study in humans that it is possible to develop an effective HIV vaccine.
The trial, conducted by a consortium of partners, including the Thai Ministry of Health and the U.S. Military HIV Research Program, used two vaccines (ALVACr HIV and AIDSVAXr B/E) that were matched to the strain of HIV that is predominant in Thailand (Clade E). The study was the first community-based trial of an HIV vaccine and involved more than 16,000 people from two provinces in Thailand. The vaccines reduced the acquisition of HIV-1 by 31.2 percent. Although this level of effectiveness did not reach the degree of protection specified in the protocol for potential licensure as a vaccine, it was statistically significant.
Thus, while the vaccine’s effectiveness is not at the level needed to control the AIDS pandemic, it is an indication that scientists will reach the goal of developing an effective HIV vaccine. By examining and analyzing the blood samples from participants, they will develop a greater understanding of how these vaccines protected some people from infection. They will build on that knowledge to create future vaccine candidates that are able to produce a greater protective effect.
Historically in vaccine development, a study will first show a modest effect at preventing disease, and then changes are made so that subsequent vaccine candidates demonstrate a more robust effect. Some of the most effective vaccines can reduce infection by as much as 95 percent, while others, like the seasonal influenza vaccine, are in the range of 50-60 percent effective. It is far easier to double the effectiveness of a vaccine from 30 to 60 percent than it is to find the vaccine with that first effect.
Moving forward toward an effective HIV vaccine will require more clinical trials in humans. Some of them will be successful, and some of them not. Hopefully, a concerted scientific effort to define the correlate of this success will lead to rapid improvements on these initial results, and bring us to an effective HIV vaccine.