While the world knows several ways of preventing transmission of HIV, a safe and effective vaccine is still lacking despite a three-decade search by scientists.

For years researchers around the world have been working on the development of such a vaccine in a challenging, step by step process. But they have reason for optimism. During this year's AIDS Vaccine 2011 conference in Bangkok from Sept. 12 to Sept. 15, scientists presented more than 400 new studies outlining advances in the search for an AIDS vaccine.

Most highlighted, however, was a further analysis of the so-called RV144 trial - the largest AIDS vaccine trial ever conducted, involving more than 16,000 volunteers in Thailand and the first trial to demonstrate that a vaccine can protect against HIV infection.

The initial findings of this RV144 Thai trial - presented in 2009 - showed the vaccine reduced the risk of HIV infection around 31 percent. These results were considered modest, yet remain the most promising so far in decades of AIDS vaccine research. To find out what exactly might have caused the modest protection, researchers then focused on identifying the responses in the immune system that correlated with the infection rate in the Thai trial.

At the conference in Bangkok, scientists presented their primary analysis results, identifying two significant antibodies, or infection-fighting protein molecules in the blood. The level of one of those antibodies was high in the Thai trial participants with low HIV infection rate. The level of the other antibody was high in participants with high HIV infection rate.

"What we not had over the past 25 years is a vaccine trial that worked and that is what RV144 did for the field in 2009,” said Barton Haynes, director of the Duke Human Vaccine Institute at Duke University of Medicine in Durham NC in the United States. “Then the next question was why did it work? So what we now have are clues as to why it might have worked and that is something that we haven't had over the past 30 years. So this is very important for the field."

The RV144 trial furthermore showed that protection reached as high as 60% in the first year after vaccination, before waning to a protection rate of 31 percent after more than 3 years. If scientists will be able to keep that initial higher efficacy, a useful vaccine might be at hand. Even a partially effective vaccine could already have a major impact and great health benefits.

The search for the vaccine is especially difficult because HIV is very diverse and mutates very quickly, with extensive variation among populations. Scientists at the conference urged that while many other (prevention) tools against HIV/AIDS are at hand, a vaccine remains the best bet in eventually eliminating the disease. Yet there is not one single bullet for HIV.

"Together the combination of treatment, prevention and a vaccine will give us the tools to ultimately control the pandemic", says Carl Dieffenbach, director of the Division of AIDS at National Institute of Allergy and Infectious Diseases (NIAID), U.S. National Institutes of Health. "The ultimate goal, the holy grail of HIV prevention, remains a safe, efficacious and durable HIV vaccine [...]. In the meantime we must continue to work towards implementing the existing prevention tools, to scale up treatment, because these are the tools that allow us to control the epidemic today, while we continue to work towards a HIV vaccine." (CNS)

(Babs Verblackt writes for Citizen News Service and is based in Thailand. Email: babs@citizen-news.org, website: www.citizen-news.org)