Determining Efficacy
The primary goal of the Phase III study is to measure how well AIDSVAX prevents HIV infection. This will be determined by comparing the number of infections in the placebo group of volunteers to the number of infections in the vaccine group.
In addition to evaluating how well AIDSVAX prevents HIV infection, data from the trials will be examined to evaluate the effect and potential benefits of the vaccine on any study volunteers who became infected with HIV despite being vaccinated.
Specifically, we will examine whether the immune system response induced by AIDSVAX:
1. Reduces the amount of HIV to undetectable levels in vaccinated volunteers who became infected.
2. Lowers the amount of virus in the bloodstream to detectable but manageable levels.
Either of these potential outcomes could represent a significant breakthrough by potentially helping HIV-infected people live longer and reduce their ability to infect others. It is not known yet whether either of these outcomes, known as secondary endpoints, would be considered for regulatory approval.
About Vaccine Efficacy
The first HIV vaccine won’t be 100% effective; few if any are. But they don’t need to be to have a major impact on an epidemic. The first polio vaccine, introduced by Jonas Salk in 1955, was only 60% effective. By the time an improved vaccine was introduced six years later, the moderately effective Salk vaccine had virtually eliminated polio in the United States, driving down the number of new infections by 96%.
Studies have shown that a vaccine that protects even 30% of the population from HIV infection could dramatically curtail the AIDS epidemic. When a portion of a susceptible population becomes immunized, their inability to infect other at-risk individuals reduces the infection rate. As the percentage of new infections decreases, so does the percentage of people who can spread the virus. This is a phenomenon known as herd immunity and it’s being used now to eradicate hepatitis B and polio.
Of course, the greater the vaccine’s effectiveness, the more quickly an epidemic can be eradicated, which is why VaxGen’s goal is to develop the best vaccine possible. It’s important to keep in mind, however, that even a moderately effective vaccine against HIV would be considered a major success. It would represent a powerful weapon against AIDS and would provide the platform from which to build even more effective formulations of AIDSVAX.
Click here for more information about determining efficacy.
