Important note: Information in this article was accurate in 2009. The state of the art may have changed since the publication date.
Bangkok Post - September 25, 2009
Apiradee Treerutkuarkul
The results of the trial carried out in Thailand released yesterday show the vaccine has 31.2% efficacy in preventing HIV/Aids infections.
Although its effectiveness did not reach the 50% efficacy rate needed to apply for a vaccine licence, and the vaccine, tested on over 16,000 volunteers in Chon Buri and Rayong, cannot lower the level of virus in the blood, the result was considered a success. 
"The outcome represents a significant finding in HIV vaccine development because for the first time ever there is evidence that an Aids vaccine has preventive efficacy," Public Health Minister Witthaya Kaewparadai said.
"Although it is not high enough for use, the result will help future vaccine research and development."
No previous vaccine trials have shown evidence of success against the virus.
Jerome Kim, deputy director (science) of the US Military Research Programme, a partner in the project, hailed the results as a big step forward.
"Although the results were modest, this is a very important scientific advance and gives us hope that a globally effective vaccine may be possible in the future," Col Kim said.
Researchers would have to determine why the vaccine worked, he said.
Other project participants are the National Institute of Health and vaccine manufacturers Sanofi Pasteur and Global Solutions for Infectious Disease.
The Thai Phase III HIV vaccine clinical trial began in October 2003.
The so-called prime-boost test combines two vaccines - Alvac, which was created by France-based Sanofi Pasteur, and Aidsvax B/E, made by Global Solutions for Infectious Disease - to stimulate different immune response systems simultaneously.
Each volunteer was given a vaccine or a placebo over a one-year period and checked after at least three and a half years.
It was controversial at the beginning mainly because of the previous failure of the Aidsvax component. Initially, the US$105 million (3.5 billion baht) project also faced a shortfall in volunteers.
Principal investigator Supachai Rerks-ngarm said infected volunteers developed roughly the same amount of virus in their blood whether they were given the vaccine or the placebo.
At the start of the trial, none of the volunteers was infected. Half received the vaccine and the rest were given a placebo. Of the placebo recipients 74 of 8,198 became infected compared with 51 of 8,197 who received the vaccine.
Two volunteers also died.
The vaccine was tested on volunteers - all HIV negative men and women aged from 18 to 30 - at average risk of infection starting in October 2003.
Dr Supachai said it would take some time before a new Aids vaccine trial would start as scientists still had to analyse what particular response was effective in the clinical trial held in Thailand.
Scientists also have to report findings on volunteers and decide if a long-term project monitoring volunteers should be carried out since the efficacy did not match the researchers' goal.
Mitchell Warren, executive director of the New York-based Global Advocacy for HIV Prevention, said talks about the effect of the vaccine were needed.
US ambassador to Thailand Eric John hoped the result would help Aids vaccine research.
"This trial will be recognised. The conclusion has brought us one step closer to Aids vaccine development."
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