HIV/AIDS: The incurable epidemic

Wednesday, December 16, 2009

FOR nearly 30 years scientists have been trying to break the back of the AIDS epidemic. Two recent studies show just how difficult and how distant that goal is.

Researchers announced Monday that their trial of a microbicide to prevent the transmission of HIV to women failed. The trial involved 9,385 women from South Africa, Uganda, Zambia and Tanzania over four years. The gel, known as PRO 20000, worked well in the lab and as part of a small trial in February. Unfortunately, it bombed in the large-scale trial. While 4 percent of those who were given a placebo tested HIV-positive, 4.1 percent of those given the microbicide tested positive.

The failure comes on the heels of the disappointment over what was believed to be a breakthrough in the development of an AIDS vaccine. In September, there was great excitement over a study funded by the National Institutes of Health whose preliminary results suggested a trial vaccine reduced the chances of HIV infection. After more than two decades of failure, a clinical trial had shown a measure of protection against HIV infection for the first time. But secondary analyses of the data published in October tempered the initial enthusiasm. The vaccine trial involved more than 16,000 people in Thailand. Over a six-year period, half received a combination of two previously failed vaccines. The other half received a placebo. In the three years after their shots, 51 participants who got the vaccine became HIV-positive, while 74 who got the placebo contracted the disease. This suggested that the risk of HIV infection was reduced by 31 percent.

Several concerns about that study existed. For instance, the vaccine was tailored to combat a strain of HIV common in Southeast Asia. So its impact on strains prevalent in Europe, North America and Africa is unknown. And there was the possibility that the success was a fluke. When only those who received all six doses on schedule are taken into account, scientists found that the vaccine reduced the risk of infection by 26.2 percent. But there was a 16 percent possibility that the results were due to chance; that percentage shouldn't go above 5.

Still, there's hope that information garnered from the experiment will be useful in developing a vaccine that works. "This is the first time that any vaccine trial in humans of an HIV vaccine has shown any positive effect, very modest thought it was," Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told us. "In my mind, this does not constitute this vaccine as an 'effective' vaccine since the effect was so modest . However, it does now form the basis for trying to dissect out any 'correlates' of protection that we might identify and then try to optimize or maximize them in the development of future HIV vaccines."

One thing that caught our attention is this: Of the more than 16,000 people in the vaccine trial, only 125, or 0.7 percent, became HIV positive. All participants were counseled on how to protect themselves from HIV and were given condoms. (Those who contracted the disease will receive free anti-retroviral treatment for life.) While scientists continue searching for a vaccine or a cure, prevention remains paramount.

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