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Q&A: CDC's Clinical Studies of Pre-Exposure Prophylaxis for HIV Prevention: Anticipated Results and Impact

January 26, 2009

When will the results of the trials be available?

Results of the trials will not be available until sufficient data have been collected and analyzed to determine whether the drugs are safe and effective. Trial results will not be available for one to three years. Independent panels of experts will monitor the trials closely so that the trials can be concluded as soon as definitive answers are available.

If PrEP does prove to be effective at preventing HIV infection in this trial, how will the drugs be made available to people who need or want it?

If the efficacy trials in Botswana and Thailand prove that one or both PrEP drugs are effective, participants in these trials and their communities will be the first to benefit. All trial participants will receive the appropriate drugs for at least one year after efficacy is proven while CDC works with the Botswana Drugs Regulatory Unit and/or the Thai Food and Drug Administration for approval of use by the health care systems in these countries. CDC is also prepared to provide technical assistance and support to its international partners in designing PrEP implementation plans in those countries where CDC-sponsored trials are being conducted. Additionally, CDC will assist WHO and UNAIDS in their efforts to develop international normative guidelines for implementing PrEP, if proven effective.

In the U.S., CDC has begun to examine potential implementation strategies with a wide range of stakeholders. Experts are examining a number of critical issues including possible funding streams, risk assessment tools, and delivery of PrEP as part of a comprehensive prevention program. Additionally, CDC is conducting research to determine effective models for reaching the populations at greatest risk in the U.S.

If the drugs prove safe and effective in one population, will they work equally well in other populations?

CDC is conducting studies in different populations to help address this question. In general, HIV is more readily transmitted through injection drug use than through sexual exposure and more easily transmitted during rectal intercourse than during vaginal intercourse. However, the correlates of protection for various modes of transmission are not fully understood. It is therefore not known what level of antiretroviral drug activity at which sites (e.g., in the blood, the vaginal mucosa, or the rectal mucosa) will be needed to interrupt transmission. For these reasons, the efficacy of particular drugs in reducing HIV transmission in one population may not necessarily apply to other at-risk populations.

If studies show that PrEP reduces the risk of HIV transmission, will people still have to practice other risk-reduction behaviors for HIV?

Yes. Regardless of the outcome, CDC will not recommend PrEP as a first-line defense against HIV infection. Abstinence and mutual monogamy with an HIV-negative partner will remain the only 100% effective ways to prevent infection. However, if effective, PrEP could provide an additional safety net to sexually active persons at risk, when combined with reduction in the number of sexual partners, HIV counseling and testing, consistent and correct condom use, and other prevention strategies.

It is also important to remember that taking PrEP drugs will not prevent acquisition of syphilis, gonorrhea, chlamydia, herpes, hepatitis, or other sexually transmitted diseases, many of which play a role in facilitating HIV transmission or speeding HIV disease progression.

Will support for these trials take away funding from behavioral interventions?

Absolutely not. As we move forward with our search for new prevention strategies, it will be critical to determine how the approaches that are proven effective can best be integrated into programs. Effective behavior-change programs have greatly reduced the rate of HIV infection in the United States and many other nations during the past 2 decades of the HIV epidemic. Because no strategy will be 100% effective in preventing HIV infection, their future impact will ultimately be determined by how effectively strategies are used in combination to provide the greatest protection to individuals at risk.

Are physicians in certain places already prescribing the drugs being studied for HIV prevention?

While one study suggested that some gay men were using PrEP despite the lack of evidence of effectiveness, subsequent CDC studies have found such “off-label” PrEP use among gay men to be rare or nonexistent. Individuals who take HIV medications before engaging in high-risk behavior to avoid infection are doing so in the absence of clinical data demonstrating that the drugs are safe and effective, and at potentially serious risk. This is especially true if the drugs are used instead of, rather than in addition to, existing prevention methods.

That is why CDC is conducting these important trials -- to contribute to the work of scientifically evaluating the safety and efficacy of PrEP among persons who are at risk. The trials will answer important questions about the impact of a daily pill on risk behavior and help us to determine how PrEP, if effective, can be used in combination with other proven strategies.

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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
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