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VaxGen's AIDS vaccine candidate to continue in phase III human testing for one more year

October 30, 2001

29 October 2001--The independent board overseeing the human testing of VaxGen’s AIDSVAX, a candidate for a vaccine to prevent AIDS, has conducted an interim analysis of this testing and says is not yet possible to conclude if the product is effective or ineffective. Therefore, study of the vaccine will continue for another year so more data can be collected, and the question of whether AIDSVAX is effective will be revisited at the end of 2002.

What is AIDSVAX?

AIDSVAX is a candidate vaccine to prevent AIDS that has been developed and is now being tested in humans by VaxGen, a California biotechnology firm. AIDSVAX is not the only AIDS vaccine candidate in development--other research groups are pursuing other products--but AIDSVAX is the furthest along. AIDSVAX is the only preventive AIDS vaccine candidate ever to reach final stage phase III human trials, the last hurdle a vaccine must clear before it can be licensed as safe and effective for widespread use.

Like other preventive AIDS vaccines now in development, AIDSVAX is intended to be given to people uninfected with HIV, to prepare their immune systems to be able to defend against contracting the virus and developing AIDS, should they later be exposed to it.

What is the status of AIDSVAX’s development?

AIDSVAX is now being tested in a phase III human trial at a number of sites in the US, Canada and the Netherlands. The purpose of the trial is to determine whether AIDSVAX, which has proven safe in earlier trials, is efficacious in preventing HIV infection or AIDS.

VaxGen designed the phase III trial to be conducted over three years, meaning the study is not scheduled to be complete until the end of 2002. However, with this fall marking the two year checkpoint of the trial, VaxGen has released the results of a preliminary analysis. This is a common practice in phase III vaccine trials. The interim analysis of AIDSVAX was conducted so that in the event that the vaccine did show efficacy at two years, the trial could be stopped and VaxGen could speed the process of applying for licensure to market the vaccine. Because this was not the case, the trial will continue as planned until next fall.

According to the interim results, the trial has not yet yielded definitive evidence that AIDSVAX is effective. At the same time, the trial has not yet yielded definitive evidence that AIDSVAX is ineffective. In short, the data are inconclusive, and more study is needed.

(Besides the North America-Europe phase III trial, there are other human trials of AIDSVAX ongoing. VaxGen is conducting a second phase III trial of AIDSVAX in Thailand, and a phase II trial of AIDSVAX administered in combination with another vaccine candidate, Aventis Pasteur’s ALVAC, is underway in four countries. However, all of these trials are separate from the North America-Europe phase III trial, and the interim results just released apply only to this study.)

What do these interim results mean?

It is impossible to know from the interim results just released whether AIDSVAX will ultimately prove effective or ineffective in one year. The interim results are just that--interim. They say only that AIDSVAX has not demonstrated efficacy ahead of the scheduled end of the trial.

History offers little guide as to what will happen next. There are some vaccines for other diseases that, like AIDSVAX, did not demonstrate efficacy upon preliminary analysis but did by the time the trial was fully complete. On the other hand, all vaccine science is a trial and error process, and, by the admission of vaccine makers themselves, failure is much more common than success.

“It is critical that VaxGen sees this phase III trial of AIDSVAX through to its completion, as it is the only way to know whether the vaccine candidate in fact works,” says Dr. Seth Berkley, MD, President and CEO of the International AIDS Vaccine Initiative.

“However, the magnitude of the epidemic is too great to bet on only one vaccine--be it AIDSVAX or any other single approach. Instead, it is critical that the world fast-track the development of multiple promising AIDS vaccines in parallel, so that in case one proves ineffective, work on others is already underway.

“We applaud VaxGen for being the only research team ever to take an AIDS vaccine to final stage human trials. But it is a tragedy that after 20 years of AIDS, just one vaccine candidate is this far along. The world can and must do better,” Dr. Berkley says.