Insights into how the first vaccine ever reported to modestly prevent HIV infection might have worked were published online today in the New England Journal of Medicine. Among adults who received the experimental HIV vaccine during the landmark 2009 RV144 clinical trial, those who produced relatively high levels of a specific antibody after vaccination were less likely to get infected with the virus. "This analysis has produced some intriguing hints about what types of human immune responses a preventive HIV vaccine may need to induce," said National Institute of Allergy and Infectious Diseases (NIAID) Director Anthony S. Fauci. In the RV144 clinical trial, which involved more than 16,000 volunteers in Thailand, the group that received the vaccine had a 31 percent lower chance of becoming infected with HIV. Since 2009, a consortium of more than 100 scientists from 25 institutions has been searching for molecular clues to explain why the vaccine showed a modest protective effect.