INFECTIONS
October 16, 2009

New Hope for AIDS Vaccine

Research on a combined, "prime-boost" vaccine has yielded modest results in what was the largest study in AIDS research history. The approach...

There is new hope for an effective AIDS vaccine in the future, the result of recent research testing a new combination vaccine. The study involved 16,000 volunteers and is the largest in AIDS research history. Though the success of the vaccine being studied was modest, the combined vaccine approach is promising.

"[I]t's the first evidence that we could have a safe and effective preventive vaccine," said Jerome Kim, one of the lead authors on the study. Kim is a researcher with the U.S. Army, which helped fund and execute the study in conjunction with the Thailand Ministry of Public Health.

Those receiving the actual treatment method were given four 'primer' doses and two 'boosting' doses over six months.

The vaccination method the researchers employed actually uses a combination of two tactics, which are known jointly as the “prime−boost” approach. One vaccine “primes” the immune system to attack the AIDS virus by introducing three synthetic HIV genes into the body (these are altered so they cannot cause HIV in humans). The second vaccine, involving a genetically engineered form of an HIV surface protein, “boosts” the immune system’s response to the virus. Though the two vaccines have not been shown to be terribly effective by themselves, researchers wanted to try them together to see if they might be more successful as a combination.

The vaccines, or Placebo for the Control group, were given to 16,000 Thai participants, between the ages of 18 and 30, who were considered to be at average risk of developing HIV/AIDS. Those receiving the actual treatment method were given four “primer” doses and two “boosting” doses over six months. The study was double−blind, meaning that neither participants nor experimenters knew who received which treatment until the study ended. In addition to receiving the shots, all participants were also given condoms and counseled on sexually transmitted diseases.

After three years, the researchers found that 51 participants receiving the AIDS vaccines had developed AIDS, vs. 74 participants in the placebo group. These numbers indicate that individuals in the treatment group were at a 31% reduced risk of developing the AIDS virus, which indicates that the vaccine combination is considerably more effective than any have been in the past.

The researchers still aren’t sure of the exact mechanisms involved, or why the combination of vaccines worked so much more effectively than either one singly. Of the individuals affected with HIV in the treatment group, blood levels of the virus were no different from what would be expected without the vaccine – which provides another puzzle to be addressed in future studies. Much more research will be needed before the vaccine combination is ready for public consumption, but the results offer researchers some much−needed optimism that a reliable vaccine may well be possible.

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