Commen Sense About Aids-What you should know about HIV vaccine trials
AIDSVAX enters Phase III
Researchers the world over are currently trying to develop safe and effective HIV vaccines. One vaccine, named AIDSVAX, is undergoing major clinical trials in the United States and Bangkok, Thailand. The Centers for Disease Control and Prevention (CDC) in Atlanta is providing answers to common questions about AIDSVAX on the CDC Web site at www.cdc. gov. Here is some of the CDC's AIDSVAX information:
Why is the AIDSVAX Phase III vaccine trial in Thailand being conducted?
The development of an effective HIV vaccine is a public health priority throughout the world. Because no one knows for sure which vaccine or type of vaccine will be most effective, multiple vaccines are being explored simultaneously.
The AIDSVAX Phase III trial is part of that plan. VaxGen, Inc., a biomedical research company based in San Francisco, developed AIDSVAX, the candidate vaccine to be evaluated. The company will fund most aspects of the study.
Who is conducting the AIDSVAX Phase III trial?
The Bangkok Metropolitan Administration (BMA) is leading the three-year collaborative research trial. BMA is conducting the trial in conjunction with VaxGen, the Mahidol University Faculty of Tropical Medicine in Bangkok, and the HIV/AIDS Collaboration (a longstanding research collaborative between the Thai Ministry of Public Health and the CDC).
What is the trial designed to do?
The trial is designed to determine if AIDSVAX is effective in protecting against HIV infection and disease. While Phase I and II trials have already demonstrated that the vaccine is safe for use and is capable of inducing antibodies against HIV infection, it is not known if the level and type of antibodies produced will prevent HIV infection. This trial will answer that question. Large-scale human testing (called a Phase III trial) is the last and most important step in the evaluation process before a vaccine is considered for licensing.
How is the trial designed?
The trial is being conducted among uninfected injection drug users (IDUs) attending 17 drug treatment clinics in Bangkok. The design is a randomized, double-blind, placebo-controlled trial in which half of the 2,500 volunteers receive the AIDSVAX vaccine being evaluated and the other half receive placebo injections that do not include the vaccine. Neither the researchers nor the participants know which participants are in each half of the trial. To ensure that none of the participants relax their preventive behaviors, all volunteers receive extensive counseling on how to protect themselves against HIV infection, as well as explicit warnings that it is unknown whether or not this vaccine will protect them from infection.
Why is this particular vaccine being evaluated?
Thai officials chose to work with VaxGen to evaluate this vaccine because it has proven safe and effective in stimulating an immune response against HIV subtypes E and B, the subtypes most common in Thailand. If AIDSVAX proves to have a protective effect, it would therefore be effective against the subtypes causing the local Thai epidemic. AIDSVAX is also the first vaccine to receive approval for Phase III trials.
Why do only some of the participants receive the vaccine? Do the other participants get any benefit from the trial?
A placebo-controlled design (where some of the participants receive the vaccine being tested and some receive no vaccine) is currently the only scientifically sound way to determine if a vaccine works. In order to determine how effective the vaccine is, researchers will compare the rate of HIV infection in participants who receive the vaccine to the rate among those who receive the placebo injection. If people in the vaccine group have lower rates of infection than people with similar risk behaviors in the group that receives the placebo injection, then researchers will know the vaccine works. If the rates of infection are the same in both groups, researchers will know the vaccine does not work.
How do you expect to determine if the vaccine prevents infection if you are counseling everyone to protect themselves from exposure?
Health officials have an obligation to ensure that all participants benefit from proven prevention methods as we search for new ones. And while risk-reduction counseling has proven effective in reducing IDUs' risk for HIV infection, it has not proven effective in totally eliminating HIV risk. If behavior change programs were 100% effective, we would not need an HIV vaccine. Regardless of the best efforts at HIV prevention counseling, some individuals will continue to take risks. By comparing the rates of infection among those at risk in both groups, researchers will be able to determine if the vaccine helps protect these individuals from infection.
Do the participants know that some do not receive any vaccine?
Yes. Because of possible language and educational barriers, Thai health officials have worked with CDC, local clinic staff, and IDUs themselves to design an extensive process to ensure that volunteers understand what their participation in the trial means, exactly what they receive and do not receive as part of the trial, and that trial participation does not protect them from infection. Potentially eligible volunteers participate in an education session on the nature of the study (which includes a video) and then are given the opportunity to ask questions.
If participants become infected during the course of the trial, are they provided medical care?
Yes, the BMA has committed to providing medical care to any participants who become infected according to the Bangkok Metropolitan Administration Guidelines for Clinical Care of HIV-Infected Patients (27 May 1998).
Why has there been skepticism about the potential effectiveness of AIDSVAX?
The AIDSVAX vaccine was developed over a period of 10 years. The first version of the vaccine was based on only one strain of HIV. Because of the increasing genetic diversity of HIV across the globe, many believed it was important to add additional strains. VaxGen has since improved the vaccine by basing different versions of it on different strains of HIV. For use in Thailand, for example, it was necessary to add an HIV strain from the subtype E virus, which is predominant in Thailand. The vaccine used in Thailand is composed of both subtype B (MN strain) and subtype E (A244 strain) antigens. For other areas of the world where the HIV subtypes may differ, the vaccine would have to be manipulated based on the strains common in those particular areas.
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