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The Elusive AIDS Vaccine: Viread's Implications
Although Viread may represent a great step forward for AIDS research, its proven effectiveness it could be disastrous for the discovery of the HIV vaccine. As promising as it may sound, PrEP is far from perfect. Viread is very expensive, and it will provide only partial protection against HIV infection. And there remains the rather awkward fact that the vast majority of individuals who need antiretrovirals (such as Viread) to treat active HIV infections cannot afford them; currently only 7 percent of those who need these drugs worldwide are receiving them. Surely outlaying millions to provide the drug to uninfected individuals is perceived as cruelly neglectful to the sick. Other issues include patient adherence (it is unlikely that all targeted patients will take the drug correctly each day) and side effects, some such as long-term bone toxicity, can be serious.
Ultimately, a true HIV vaccine is more desirable than Viread PrEP. The right vaccine would only be administered once (or a few times), greatly lowering cost and eliminating adherence problems. For this reason, a vaccine could potentially be deployed on a much greater scale than Viread, resulting in a deeper impact on the epidemic.
Unlike Viread, of course, no vaccine for HIV exists yet. As it stands, the vaccine remains a formidable scientific challenge and most experts estimate it will not be available for a decade at the very least. But vaccines promise the best potential for tackling the HIV/AIDS epidemic. And many scientists and other interested parties seem to envision PrEP as a useful "stepping-stone" - an interim control while a vaccine remains in the works.
But if Viread is proven effective, the search for a vaccine may be in serious trouble. For ethical reasons, all participants in vaccine trials must receive access to all available prevention methods available. Right now, that means participants must be given comprehensive prevention counseling and free access to condoms and clean needles. If PrEP were proven effective, it would have to be provided too - for every participant in any vaccine trial.
The costs and administrative difficulties of distributing a once-daily pharmaceutical to thousands of participants could render vaccine trials inoperable. On top of that burden, sample sizes for studies would have to broaden to compensate for Viread's effect. Developing vaccines is already expensive, with so little as a predicted return that the pharmaceutical industry neglects them in favor of developing new drugs. The development community has responded by producing various incentive schemes to stimulate vaccine development, but the immense burden that Viread creates would almost certainly override the reach of these incentives.
What the Future Holds
What does all this mean for the ongoing investigation into Viread's potential as a preventive agent? Could anyone advocate abandoning an effort that could save so many lives?
Of course not. But the challenges involved need to be explored in far greater detail. It would be irresponsible to portray Viread as a solution to the problem of AIDS when it is, in itself, riddled with problems. There needs to be greater clarity about the guidelines of a trial, informing better debate about the ethical implications for those involved. Additional discussion also needs to focus on how to distribute Viread in a simple and cost-effective manner. Addressing these problems will require increased information-sharing, commitment, and funding. There needs to be a much more effective advocacy machine on AIDS prevention, one that fully incorporates the likely success of the Viread trials. Simply generating more money does not automatically eliminate all difficulties, but increased funding, combined with awareness and political support, could greatly alleviate both the problems described here.
Overall, these concerns should be interpreted as a plea for caution, not a condemnation of the PrEP effort. Attempts to find effective weapons against the epidemic should be applauded, but they should never be adopted without serious analysis. Unveiling an apparent "magic bullet" like Viread, without first engaging in a much more thorough and coordinated exploration of some of these issues, could have tragic implications. Viread is a tool in an arsenal, and it is critical that we retain a sense of humility if we are ever to make real progress against what may be our most powerful foe.
Sources
1. Gilead Sciences, Gilead Sciences Annual Report 2003, available at http://co2.mobular.com/ccbn/7/522/571/.
2. C.C. Tsai et al, Prevention of SIV infection in macaques by (R)-9-(2-phosphonylmethoxypropyl)adenine, Science 270(5239): 1197-1199, 17 November 1995.
3. Gilead Sciences, Viread: full prescribing information, available at http://www.gilead.com/pdf/viread_pi.pdf, 2003.
4. Kaiser Daily HIV/AIDS Report, "Cambodian sex workers refuse to participate in clinical trial of antiretroviral drug without insurance for side effects," available at http://www.kaisernetwork.org/daily_reports/rep_index.cfm, 30 March 2004; Ibid, Cambodian Prime Minister orders stop to human clinical trial's of Gilead's Viread," available at http://www.kaisernetwork.org/daily_reports/rep_index.cfm, 12 August 2004; S. Russell, "Prostitutes protest AIDS-drug test: Bay Area company hit with charges of exploitation," San Francisco Chronicle, A1, 14 July 2004.
5. UNAIDS, "Global summary of the HIV and AIDS epidemic in 2003," available at http://www.unaids.org/en/resources/epidemiology/
epicorejuly2004.asp.
6. Gilead Sciences, Viread: full prescribing information.
7. See R. Horton, "AIDS: the elusive vaccine," New York Review of Books 51(14), 23 September 2004.
8. UNAIDS, "Ethical considerations in HIV preventive vaccine research," prepublication version.
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