BARCELONA, Spain -- The U.S. and Thai governments will soon begin the largest trial yet of a preventive AIDS vaccine, testing a combination of vaccines on more than 16,000 subjects in the general Thai population, researchers from the two countries announced Monday at the 14th International AIDS Conference.
The trial, originally sponsored in a slightly different form by the Department of Defense, was canceled in February. After a small reconfiguration to change its goals, the $36 million effort will now be funded by the National Institute of Allergy and Infectious Diseases, which has taken over the AIDS programs formerly operated by the military.
There has been much debate over when new candidates should be tested and what criteria should be used, said institute director Dr. Anthony Fauci. "But at the end of the day, we have to have candidates in trials. Even if they fail, we will learn things that are very important."
In another development, Brisbane, Calif., biotechnology company VaxGen Inc. said that a commercial AIDS vaccine could be available by 2005 if two major trials now nearing completion are successful.
Although data from VaxGen's trials of 7,900 subjects will not be available until early in 2003, experts said the mere fact that the trials were successfully carried out represents a substantial step forward in the quest to control the AIDS virus, which is expected to have infected 110 million people by the year 2020.
Critics had argued that it would not be possible to complete the study because of the difficulties involved in monitoring large numbers of high-risk patients for three years or longer, but such fears have proved groundless.
"Just the fact that they pulled this off is reason for optimism," said Dr. Carl Dieffenbach of the National Institute of Allergy and Infectious Diseases. Nonetheless, critics cautioned that AIDS vaccines have offered high promises in the past, only to have the hype unfulfilled.
Researchers have been searching for a preventive AIDS vaccine since AIDS was first recognized 21 years ago. "An effective vaccine is our only hope of stemming the epidemic," said Sandra L. Thurman, president of the International AIDS Trust.
More than 30 candidate vaccines have already been put through phase 1 and phase 2 clinical trials, designed to test safety and to determine if they have any efficacy at all. Eight are currently undergoing such trials.
A classic vaccine
But the VaxGen product, called AIDSVax, was the first to enter phase 3 trials, the final large trials required before a new drug or vaccine can be approved by a regulatory agency.
AIDSVax is a classic vaccine much like those used to control polio, measles and a host of other infectious diseases. Viral surface proteins produced by genetic engineering techniques are administered to stimulate production of antibodies that will attack viruses before they can invade cells.
"Antibodies protect against viral infection, we know that," said Dr. Donald P. Francis, CEO of VaxGen. "Everyone who gets the vaccine develops an immune response. The question is, does it last long enough and provide protection?"
VaxGen is sponsoring two trials, one in North America and the Netherlands involving 5,400 people who are at risk of contracting the virus through sexual transmission, and one in Thailand involving 2,500 intravenous drug abusers. In each group, half receive the vaccine and half a placebo.
Francis said that, despite rumors to the contrary, VaxGen had received absolutely no hints at all about the potential results of the trials. He called such rumors "hogwash."
What they do know, he added, is that the safety data monitoring board, which oversees the trial, has said that there are sufficient numbers of infections in the placebo group to indicate that the trial will provide a result.
No one expects the vaccine to be 100 percent successful. But extensive modeling studies have indicated that even a 30 percent efficacy would be enough "to drive the epidemic into the ground," he noted.
"A little bit of immunity goes a long way," Dieffenbach said.
"If we get a 30 percent efficacy, I'll be thrilled," Francis added. "Once we have some efficacy, we can always increase it."