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Sunday, December 6, 2009

Hope for an HIV Vaccine?

HIV Vaccine Provides Modest Benefit

The quest for an effective vaccine against HIV resembles a search for the Holy Grail. That's what I quip on this week's podcast, and while the phrase is tired and shopworn, in this case it fits. We've known about the cause of AIDS for decades now, the virus continues to kill tens of thousands annually, and although we have very effective drugs that keep the virus in check they are too expensive to offer much solace to much of the world's HIV infected population. In this week's NEJM, a glimmer of hope is reported: Vaccination With ALVAC and AIDVAC to Prevent HIV-1 Infection in Thailand.

Thailand is a country with a large population of both HIV infected people and those at risk for contracting the virus. Investigators evaluated over 16,000 volunteers who received multiple injections of the vaccine. Each volunteer was monitored for whether they became infected with HIV at the end of the six month vaccination series, and again at six month intervals for three years.

A couple of things are worth mentioning about the study subjects: they were not infected with HIV at the beginning of the study but were at risk for infection, either because they were sexual partners with someone who was already infected, they used IV drugs, shared needles, frequented commercial sex workers and the like. Subjects were categorized for whether they were at low, moderate or high risk for contracting the infection, and they were largely heterosexual.

At the end of the study, the vaccine was about 30% effective in preventing infection with HIV, depending on how the analysis was done. While this is not a great result, it's the best we have so far and the study tells us some very important things. First of all, traditional measures of vaccine efficacy don't apply in this case. Vaccination didn't impact on how many viruses were found circulating in the blood of those who subsequently became infected, nor did it have any effect on CD4 cells, the critical immune cell depleted by HIV. We also learned that multiple vaccinations were required. But it is a positive step and that's worth celebrating.

It's also important to mention that this study didn't go forward the way most do in that volunteers were not recruited, given the vaccine and then deliberately exposed to HIV, the way we assess many other vaccines. Clearly such a protocol would be unethical.

Other podcast topics this week include use of left ventricular assist devices in folks with heart failure, also in NEJM, aspirin use in those with stomach ulcers and consideration of a new bug in sore throats in young adults in Annals of Internal Medicine. Until next week, y'all live well.

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