Research led by CHP/PCOR acting director Douglas K. Owens, presented in late May at an international AIDS conference, has found that even if an HIV vaccine were only modestly effective -- even if it protected against HIV/AIDS just 50 or 60 percent of the time -- the vaccine would yield substantial health benefits and would save millions of dollars by preventing new HIV and AIDS cases.

The findings could help developers of HIV vaccines determine whether it makes sense to proceed with further clinical trials. And once an HIV vaccine becomes available, the findings could help policymakers determine how the vaccine should be administered -- who should receive it, when and where it should be given, how much it should cost, and who should pay for it.

"We asked the question, 'How good would an HIV vaccine need to be, to be cost-effective?'" Owens said. "The answer -- which was somewhat surprising -- is it doesn't need to be all that effective."

Owens presented the research at the 12th International Conference on AIDS, Cancer and Related Problems, held May 24-31 in St. Petersburg, Russia. The study is part of a larger multi-center research project he is leading, called "Making Better Decisions: Policy Modeling for AIDS and Drug Abuse."

Although no proven HIV vaccine currently exists, more than 20 vaccines are in clinical trials around the world, and many HIV/AIDS researchers -- Owens among them -- are hopeful that an effective vaccine will someday emerge. Two types of vaccines are possible: a preventive vaccine, which would protect recipients from being infected with the HIV virus if they were exposed to it, and a therapeutic vaccine, which would prevent HIV-positive individuals from developing AIDS, or would halt or slow the disease's progression.

Absent an existing vaccine, Owens and colleagues used modeling to calculate the benefits that would come from using different types of vaccines under different conditions. The factors considered include the cost and effectiveness of the vaccine and the type of individuals receiving it. The researchers found, for example, that a preventive vaccine that is 75 percent effective would prevent 5,000-10,000 HIV infections over 20 years, in a population of about 47,000 sexually active homosexual men, and would thereby save almost $150 million in future AIDS treatment costs.

The savings are significant despite the high cost assumed for the vaccine -- about $1,000 per dose. Owens' study is one of the first to comprehensively examine the costs and benefits of potential HIV vaccines.

Owens and his colleagues were initially surprised at how cost-effective the vaccine appeared to be, but upon further reflection, he said, "it made a lot of sense when you consider the high mortality of HIV infection and how expensive it is to treat."

Owens noted that the findings apply only to the population examined in his study -- sexually active homosexual men in San Francisco -- and that the impact of a vaccine could be quite different in other populations. Owens is also studying the impact of an HIV vaccine on injection drug users in Thailand.

One critical factor determining the population benefit of a therapeutic vaccine, Owens found, is its effect on infectivity -- the extent to which the vaccine can prevent an HIV-positive individual from transmitting the virus to others.

Owens emphasized that the research from the "Making Good Decisions" project is designed to yield practical information that can help guide policy decisions. "A lot of studies examine preventive interventions like condom distribution programs, but they only tell you how their program affects specific behaviors, such as rates of condom use," Owens said. "Our goal is to use the results of these studies to assess the health outcomes that matter most: How does the intervention affect HIV transmission rates and the number of new AIDS cases?"

Owens emphasized that cost-effectiveness studies do not yield a yes-or-no determination on whether an intervention is cost-effective. Instead, the studies produce information on the costs and benefits of the intervention, with the goal of helping decision-makers determine whether implementing the program would be worthwhile. "These are value judgments based on how much society is willing to spend to prevent illness or death," Owens said.

"Making Better Decisions: Policy Modeling for AIDS and Drug Abuse" is funded by a grant from the National Institute on Drug Abuse (NIDA project officer Peter Hartsock, PhD). Findings from the project have been published in numerous journal articles and have been presented to the World Health Organization and the U.S. Centers for Disease Control and Prevention.