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Experimental AIDS Vaccine May Increase Risk of HIV

By Brandon Keim

The frustrating saga of AIDS vaccines -- 22 years of research, and not a single one yet works -- has taken a sad turn: an experimental vaccine developed by Merck may leave people more vulnerable to HIV infection.

The Washington Post reports that 19 South Africans who received the vaccine during a clinical trial have contracted the virus, compared to 11 people who received a placebo. Investigators are contacting participants to let them know whether or not they received the vaccine.

The trials, which began in December 2004, were not limited to South Africa, but included 15 U.S. cities, along with sites in Peru, Brazil, Australia, Haiti, the Dominican Republic and Jamaica. Those participants have not yet been told whether they received the vaccine; researchers will meet in November to decide whether the South African results are an aberration or indicative of a fundamental flaw in the vaccine.

It's possible that the infections were purely coincidental. It's also possible that the vaccine "could have caused immunological changes that made it easier for the virus to take hold during a later exposure."

This is a major setback for not only for Merck's vaccine, which was developed in conjunction with the NIH, but for the entire AIDS vaccine field. The Post notes that "researchers worldwide considered it the most promising candidate yet in a multibillion- dollar quest for an AIDS vaccine dating to the 1980s."

Why have AIDS vaccines proved so difficult to develop? An article published several years ago in PLoS Medicine discusses the many reasons -- the virus's hardiness, its uncanny ability to adapt to not only drugs but immune responses, and our own incomplete understanding of it. But some people are able to resist infection despite repeated exposures; and some are able to control the virus spontaneously. A vaccine is possible. And someday we'll find it.