September 2, 2003
The studies, begun in late 1999, explore the vaccine's safety and any immune response -- not whether the vaccine prevents people from getting the disease. Results are expected next year. If test results are promising, studies on the vaccine's effectiveness in humans could take another few years, until 2008 or 2009.
Merck's lead vaccine uses a common-cold adenovirus to carry genetic material from HIV into the body in order to produce an immune response. In Merck's monkey studies, a "naked DNA" inoculation with an adenovirus booster produced the best immune response. Those monkeys were not virus-free, but virus levels remained low and the animals did not get AIDS.
"The real question is: If you can elicit this kind of response in monkeys, will it make any difference in humans?" asked Emilio A. Emini, Merck's senior vice president of vaccine and biologicals research. "And if it does make a difference in natural HIV selection -- and I think it will, and most people believe it will -- what's going to be the nature of that difference?"
Phase III AIDS vaccine trial results from the biotech company VaxGen, released in February, showed that its vaccine did not protect most people from the disease. The company expects to release results of a second large Thailand study later this year.
"I am really optimistic that we can make a difference against HIV eventually," said Pat Fast, medical director at the International AIDS Vaccine Initiative, which is supported by private donations from the World Bank, the Bill and Melinda Gates Foundation and others. "It's hard to put a time line on it," Fast said. Experts believe vaccines are the only way to stop the global AIDS epidemic.