Scientific and economic issues remain a challenge for the development of a successful HIV vaccine, said Dr. Larry Corey, who described the effort as a "marathon, not a sprint" in a plenary session at the 14th International AIDS Conference.
Despite these barriers, a new generation of vaccines designed to illicit an immune reaction known as a T-cell response are likely to enter large-scale clinical trials in the next two years.
Such vaccines, rather than protecting the uninfected from subsequent HIV infection, would be used to reduce the levels of virus in those who become infected following vaccination. These vaccines would, therefore, be likely to help infected individuals stay healthier longer and be less likely to transmit HIV infection to their sexual partners.
Among the scientific obstacles to HIV vaccine development is that unlike infectious organisms against which effective vaccines have been developed, parts of the HIV virus most responsible for provoking an immune response remain mysterious. Also, the virus has many strategies to escape immune-system control, including an ability to mutate rapidly within the body.
A high-risk venture
Corey described vaccine development as a high-risk scientific venture, which makes the effort less appealing to the pharmaceutical industry.
"Vaccines need to be highly effective, have negligible toxicity and be inexpensive," he said. "Therefore, they compete poorly for company resources."
Among the hopeful developments, he said, is that economic perceptions have begun to change. In the last five years, public and private funding as well as political support for vaccine research has increased.
In addition, several prominent economists have shown that poor health has a significant impact on a nation's economic development.
Vaccine development has proceeded slowly in part because studies to assess the vaccine's ability to limit disease transmission in a population typically have been conducted only after clinical trials for vaccine efficacy are completed.
"While we continue to see five million new cases of infection a year, this sequential process is unacceptable," Corey said. "We are designing new trials to do population-based studies in the context of a phase III vaccine trial."
Vaccine development must proceed with a larger prevention effort and doesn't compete with other prevention strategies, Corey said. He called on countries, particularly those with new epidemics, to consider participating in vaccine trials and for enhanced cooperation among researchers, governments and communities.
"The virus recognizes the similarity among people on this planet," he said. "Scientists, policy makers and communities must act similarly."