The $36 million study will take five years, said Vallop Thaineau of the Thai Ministry of Health, and is expected to begin before the end of 2002 if regulators in the United States and Thailand approve. It will be the largest study of an AIDS vaccine to date, although two smaller trials -- sponsored by VaxGen Inc., of Brisbane, Calif. -- are expected to be finished within months. VaxGen is also involved in the new Thai study.
The study is a Phase III trial, in which researchers attempt to determine whether an experimental drug actually affects the outcome of a disease. A U.S. Phase III trial of a similar AIDS vaccine was canceled at the beginning of this year, but Thaineau said the cancellation "in no way affects our decision to move forward" because the decision was based on technical grounds.
Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, said the previous Phase III trial was canceled because earlier phases failed to meet a pre-set laboratory standard, not because of concerns about the drug's safety or effectiveness. By contrast, he said, the Thai trial will observe people who have been given the vaccine to see if it protects them against the disease.
"This is a safe vaccine," Fauci said. "The question is, will it work."
Jim Tartaglia, head of research for Aventis Pasteur Inc., in Lyon, France, which is making part of the vaccine to be tested, told United Press International the U.S. trial was intended to examine how the vaccine works. "Now we're looking at whether it works," he said.
Thaineau said the 16,000 healthy volunteers will be selected randomly to receive either the vaccine or a non-active placebo. After five years, researchers will see which group had more HIV infections. The vaccine itself will be given in two stages. The first will "prime" the immune system, and the second will "boost" the effect, he said. Aventis Pasteur is making the first-stage vaccine, while VaxGen is making the booster.
VaxGen's booster is already in a Phase III clinical trial in Thailand, involving 2,500 injection drug users, who are considered to be at high risk for HIV. That trial should be finished late next year, VaxGen President Donald Francis said Monday.
A similar VaxGen vaccine, targeting a slightly different HIV strain, is expected to deliver Phase III results before the end of 2002, Francis said. "We will have an answer as to efficacy of this vaccine within months," he said.