It is for the first time that a vaccine has shown signs of protection against the disease in the clinical trials, and the scientists are hoping that the results of the clinical trial will have "important implications for the design of future HIV
vaccines".
For the purpose of the trials, 16,000 volunteers were chosen from a cross-section of the Thai young adult population, aged 18 to 30, and not just high-risk groups like the sex workers.
Prior to the vaccination, all the participants were given condoms, counseling, and treatment for any sexually transmitted infections.
Half of the volunteers were given six doses of two vaccines in 2006 and half were given placebo shots- meaning those who weren't given the active drug, informed Col. Jerome H. Kim, a physician and manager of the army’s HIV vaccine program.
The two-vaccine drug was used as a “prime-boost” strategy, wherein the first one primes the immune system to attack HIV virus and the second one strengthens the response.
Then, they were tested after every six months for HIV, and those who became infected were given free treatment.
Study’s findings
The medical condition of the volunteers was followed for three years. Out of those who got placebos, 74 became infected, as compared to only 51 of those that were given the vaccine shots.
The researchers maintain that the difference was statistically significant and indicated that the vaccine was 31.2 percent effective.
However, the results showed that all the infected people developed roughly the same amount of virus in their blood whether they got the vaccine or a placebo.
This suggested that the vaccine RV 144 did not produce neutralizing antibodies in the immune system as most vaccines do, rather they found that it prevented the HIV infection from spreading further.
Why the two-vaccine drug worked is still not clear
The vaccine known as RV 144 is a combination of two genetically engineered vaccines; ALVAC, developed by the vaccine division of France's Sanofi-Aventis, and AIDSAX, made by Global Solutions for Infectious Diseases, a non-profit group in US formerly known as VaxGen.
The two vaccines when tested individually in earlier trials did not show any ability to protect a person against HIV. Therefore, the scientists are still not sure why the vaccine RV 144, a combination of these two, had worked.
Nevertheless, the researchers believe that the results are very encouraging and that development of a safe and effective preventive HIV vaccine is possible. However, they maintained that further study is required to build upon these findings.
"Conceptually, we now know a vaccine is possible," said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases which funded the six-year trial.
"Whether the vaccine is going to look anything like this one I don't know. But at least we know it can be done," he added.
The United Nations agency, UNAIDS, estimates that every day 7,500 people worldwide become infected with HIV.
The study has been sponsored by the U.S. Army and conducted by the Thailand Ministry of Public Health.
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