PrEP strategy could dramatically slow the spread of HIV

Sep 20 2007

Giving a daily antiretroviral pill to people to prevent HIV could profoundly slow the spread of the infection in sub-Saharan Africa, where it is a full-blown epidemic, University of Pittsburgh School of Medicine researchers report.

Published by the Public Library of Science in the Sept. 19 issue of PLoS ONE, the findings are based on a mathematical model developed by the researchers to predict the public-health impact of pre-exposure chemoprophylaxis (PrEP) – an HIV prevention strategy that uses antiretroviral drugs, currently given in combination to treat HIV-positive individuals, to stop the infection from occurring in the first place.

Through the model, the research team predicts that PrEP, targeted to those at highest behavioral risk, could have a major impact on public health, potentially preventing 3.2 million cases of HIV in southern sub-Saharan Africa alone in 10 years. Sub-Saharan Africa, the epicenter of the HIV/AIDS global epidemic, contains almost 63 percent of the world's HIV-infected population, totaling about 22.4 million adults.

PrEP is based on the hypothesis that HIV transmission can be curtailed if treatment is given before exposure to the infection occurs. Data from animal studies suggests that PrEP is an effective method to prevent HIV infection and it is now under study in human populations. The strategy has its detractors, however, who suggest that the availability and use of PrEP could cause sexual disinhibition in which individuals feel as though they no longer need to practice traditional methods of safe sex, including abstinence, using condoms and limiting sexual partners.

“We know that antiretroviral drugs given at or shortly after exposure can reduce the risk of HIV infection,” said Ume Abbas, M.D., lead author and assistant professor, University of Pittsburgh School of Medicine. “While the ongoing PrEP studies in humans are extremely important, they are not designed to look at the potential public health impact of PrEP. What we hoped to answer with our study is whether there is a potential population-level benefit from PrEP in reducing rates of HIV transmission. We found a substantial benefit can be gained from PrEP, indicating it may play an important role in our arsenal of HIV-prevention strategies.”

The researchers studied three scenarios within the model – an optimistic scenario in which they assumed PrEP was effective 90 percent of the time and used by 75 percent of the sexually active population; a neutral scenario in which PrEP was effective 60 percent of the time and used by 50 percent of the sexually active population; and a pessimistic scenario in which PrEP was effective 30 percent of the time and used by 25 percent of the sexually active population.

They found a significant public health benefit from PrEP in the optimistic scenario that could potentially cut new HIV infections by 74 percent in sub-Saharan Africa, if used consistently for 10 years. The benefits in the neutral and pessimistic scenarios were significantly lessened – a 24.9 percent reduction in infections was noted in the neutral scenario and a 3.3 percent reduction was noted in the pessimistic scenario.

“Our data highlights the enormous potential public health benefit of pre-exposure chemoprophylaxis against HIV, provided the regimen is efficacious and used consistently daily for a number of years,” said John Mellors, M.D., senior author of the study and professor, University of Pittsburgh School of Medicine and University of Pittsburgh Graduate School of Public Health.

The researchers also looked at the cost-benefit of distributing PrEP and found that targeting it to individuals who were the most sexually active and thus at the highest risk for HIV infection, produced a significant decline – 28.8 percent – in infections at a much lower cost than distributing PrEP to the general population.

To address the issue of sexual disinhibition, the researchers assumed a 100 percent increase in risky sexual behavior and observed that while the beneficial effect of PrEP in the optimistic scenario declined when an individual became sexually disinhibited, there was still a notable reduction of HIV infections in the range of 23.4 to 62.7 percent.