This is amazingly good news.
The result came after the world's largest Aids vaccine trial of more than 16,000 volunteers in Thailand.
Recent failures led many scientists to think such a vaccine might never be possible.
Even though the benefit is modest, "it's the first evidence that we could have a safe and effective preventive vaccine", military spokesman Jerome Kim said in a telephone interview. He helped lead the study for the US Army, which sponsored it with the National Institute of Allergy and Infectious Diseases.
