Senior Associate, Global Health Policy Center, CSIS
We have known for some time that among people infected with HIV, those with higher concentrations (“viral load”) of HIV in their blood are more likely to transmit HIV to others during sexual intercourse. One of the dramatic effects of taking anti-retroviral drugs (ARVs) is a significant decrease in “viral load,” and there had been recent speculation that having HIV-infected people taking ARVs early might reduce their chance of transmitting HIV to their uninfected sexual partners. This concept is called “Treatment as Prevention”.
In a significant development, in May 2011 an HIV transmission study (called “HPTN 052”) addressing just that question was stopped early because the HIV prevention impact of taking ARVs -- a startling 96% reduction in HIV transmission to sexual partners -- was so convincing to the outside scientific group monitoring study results.
This provides the backdrop for this week’s International AIDS Conference being held in Washington, DC. In fact, the conference title is “Turning the Tide Together” which relates specifically to the hopes around using treatment as prevention.
However, public health experts are divided about the reality of turning those remarkable scientific results into effective and high coverage country-level programs any time soon. Conference attendees and others who follow these issues in the media are likely to hear strong opinions on both sides about how quickly the many implementation challenges can be addressed. The following is a list of only some of the challenges that need to be addressed before widespread use of “treatment as prevention” can be recommended:
Scientific and biologic challenges
- The greatest risk of transmitting HIV to others is in the first 6-8 weeks after infection, a time when viral load is very high; that 6-8 weeks is also the period before an HIV test would turn positive. How can that “window period” be addressed?
- Resistance of HIV to the effects of ARVs develops relatively quickly once ARVs are introduced in widespread use in a population. If ARVs are used more widely in prevention programs, will population-level drug resistance develop and spread even more quickly?
- Co-infections with infections such as malaria and tuberculosis increase the body’s HIV viral load. Will ARV use in co-infected people still have the same striking prevention effect or will those co-infections facilitate HIV transmission anyway?
- Behavioral disinhibition is an increase in sexual risk behaviors that could occur in people who are aware of the prevention benefits of ARVs that they are taking. How often will that occur and how can its impact on HIV transmission be minimized?
- In many recipients, ARVs cause side effects that may be severe or unpleasant enough to convince some people to stop taking ARVs. If more people take ARVs for longer periods, even more side effects are likely to occur. What will be the impacts of those side effects on people’s willingness to take ARVs every day - to protect others - when they don’t feel sick themselves?
Programmatic and Logistical Challenges
- Early identification of individuals at high risk of acquiring or transmitting HIV requires identification of discordant couples. How will creation of safe and effective couples’ programs of HIV testing and counseling be accelerated in populations where they do not now exist?
- Currently, HIV-infected people in some key sub-populations (e.g., people who inject drugs, men who have sex with men) in some countries have lower ARV treatment coverage than HIV-infected people in less stigmatized populations of those countries. How will such critical inequities of ARV access be addressed in Treatment as Prevention programs?
- What are the guidelines under which Treatment as Prevention programs will be monitored and evaluated?
- Adding new programs that recruit new ARV patients will require lots of new resources. Where will money come from to pay for the extra ARVs? Where will the trained staff come from to run TasP and other programs?
- In many countries, ARV waiting lists of sick HIV-infected people already exist. How can Treatment as Prevention programs be implemented in a way that does not add further delays for those on waiting lists?
Life would be simpler if we could move directly from a demonstration of the high efficacy of a biomedical intervention to the widespread use of that intervention in real world settings. Unfortunately, such interventions first have to be demonstrated to be acceptable, feasible and effective in terms that make sense to funders, policy-makers, program implementers, and potential beneficiaries. Hopefully, Treatment as prevention can keep moving in that direction.