FLORENCE, Italy -- Participants were jubilant on the eve of last year's International Conference on AIDS. For the first time, it seemed possible to develop a human vaccine against the epidemic because immunized animals had been protected against the AIDS virus.
As scientists gather today for this year's conference on acquired immune deficiency syndrome, the mood is still upbeat but tempered by obstacles to making a completely preventive vaccine useful under conditions in the field.
"What we've learned in the last year, 80 percent to 90 percent, has really increased our optimism," said Dr. Wayne Koff, head of the AIDS vaccine development for the National Institutes of Health.
"Yet," he added, "there have been one or two occasions of breakthrough [of the AIDS virus] in monkeys and apes that we thought were protected. It just shows you can't be naively optimistic."
Ten vaccines are in clinical trials in the United States, Europe and Africa, and five other products are in preclinical testing in animals, Dr. Koff said.
Although no product has produced the kind of immune responses seen with the polio or smallpox vaccines, results have been positive enough to propel researchers and health agencies to field trials.
"In a year, I think we will be in large-scale efficacy trials for vaccines," Dr. Koff predicted.
Dr. Michael Merson, head of the World Health Organization's Global Program on AIDS, said that the 10 potential vaccines "seem to be safe. And I think if we're lucky, many of them will be ready for field trials in the next few years. They will be worthy of testing on man." Behind the term, "large-scale efficacy field trials," lie enormous logistic and ethical dilemmas. To test the efficacy of a vaccine, people must be exposed to the live virus, which means they could get AIDS if the experiment fails. The World Health Organization is setting up vaccine trial sites in 14 developing countries in which AIDS is rampant. Researchers expect useful results from the controlled trial, which will follow thousands of vaccinated and unvaccinated volunteers in a high-risk area for four to five years, Dr. Merson said. He declined to name the 14 countries.
But people who are vaccinated will forever test positive for human immunodeficiency virus infection, even though they do not carry the virus, because the AIDS test measures the presence of anti-HIV antibodies.
Vaccines are being developed with two different strategies in mind: prevention and therapy. Preventive AIDS vaccines would have to block HIV infection completely. Because of the near-100 percent mortality of AIDS, no partially protective product would be likely to get Food and Drug Administration approval.
A therapeutic vaccine would be given to people infected with HIV in hopes of boosting their immune responses and would not have to meet as high a standard of efficacy as a preventive product.