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Model of pre-exposure prophylaxis against HIV forecasts benefits, potential cost-effectiveness

February 10, 2009

NIAID Media Availability

WHAT: For every two people who begin treatment for HIV infection globally, five others become newly infected. Therefore, preventing new HIV infections is the foremost strategy for ending the HIV/AIDS epidemic. One potential prevention strategy involves giving antiretroviral drug regimens to people who are at high risk for HIV to protect them from infection. Important questions about this experimental approach, known as pre-exposure prophylaxis (PrEP), remain unanswered, including, Could PrEP cut the lifetime risk of HIV infection? Would PrEP be cost-effective?

A new mathematical model of PrEP use in U.S. populations at high risk for HIV infection takes these and other questions into account and predicts the prevention strategy could substantially reduce the lifetime risk of HIV infection. According to the model, the cost-effectiveness of PrEP could vary substantially depending on the age of the target population, their risk behaviors, the annual rate of new HIV infections in the target population, and the efficacy and cost of antiretroviral PrEP drugs. These findings are reported by a team of scientists led by A. David Paltiel, Ph.D., of Yale University, and supported by the National Institute of Allergy and Infectious Diseases (NIAID), the National Institute of Mental Health and the National Institute on Drug Abuse, all part of the National Institutes of Health.

Dr. Paltiel says his team's model is the first to establish performance benchmarks that clarify the clinical, epidemiologic and economic circumstances under which PrEP would represent good patient care, good public health and good value.

To create their model, the researchers made several conservative assumptions: 1) PrEP is 50 percent effective; 2) the target population is American men who have sex with men who average 34 years of age; 3) 1.6 percent of this population becomes newly infected with HIV annually; and 4) the antiretroviral drugs (tenofovir and emtricitabine) cost $9,000 per year. With these parameters, the model predicts PrEP would cut the lifetime risk of HIV infection from 44 percent to 25 percent. However, the life expectancy of the target population from the time after beginning PrEP would increase by less than a year (from 39.9 years to 40.7 years) and PrEP would not be cost-effective by current U.S. standards. Yet with modest improvements in the efficacy of antiretrovirals used preventively, more realistic estimates of their cost (potentially as low as $900 per year), or a target population that is younger and at higher risk, the model predicts PrEP might be as cost-effective as other widely recommended public health and medical interventions in the United States. With large improvements in these parameters, the potential benefits of PrEP could be substantial, according to the model. For example, assuming PrEP will be 90 percent effective leads the predicted lifetime risk of HIV infection to fall from 44 percent to 6 percent.

NIH/National Institute of Allergy and Infectious Diseases