For the first time, an HIV vaccine trial has produced positive results: A new vaccine tested on more than 16,000 volunteers in Thailand reduces the risk of HIV infection by more than 30 percent, The New York Times reports. The clinical trial—the largest HIV vaccine trial in history—was backed by the National Institute of Allergy and Infectious Diseases (NIAID), the Thai Ministry of Public Health, the United States Army and patent-holders to the two parts of the vaccine, Sanofi-Pasteur and Global Solutions for Infectious Diseases.

According to the article, the vaccine—known as RV 144—is a combination of two genetically engineered vaccines, Alvac-HIV and AIDSVAX, which previously have not worked in humans. The researchers are unsure as to why these vaccines worked so well in tandem.

“I don't want to use a word like ‘breakthrough,' but I don't think there's any doubt that this is a very important result,” said NIAID director Anthony S. Fauci, MD. “For more than 20 years now, vaccine trials have essentially been failures. Now it's like we were groping down an unlit path, and a door has been opened. We can start asking s ome very important questions.”

Col. Jerome H. Kim, MD, manager of the Army's HIV vaccine program, said half of the 16,402 volunteers were given six doses of two vaccines in 2006 and half were given placebos. They were given regular HIV tests for three years. Of those who received placebos, 74 contracted HIV, while only 51 of those who got the vaccines did. Kim said those statistics show the vaccine is 31.2 percent effective.

While Fauci said that officials would never license a vaccine less than 70 or 80 percent effective, he added, “If you have a product that's even a little bit protective, you want to look at the blood samples and figure out what particular response was effective and direct research from there.”

“This is not the endgame,” Fauci said about the latest findings. “This is the beginning.”