In one of the studies, 49 of 914 men who received the vaccine became infected with HIV, while only 33 of the 922 men who got dummy shots became infected. And in another trial, 24 of 741 volunteers who got the vaccine developed HIV, compared to 21 of 762 participants who got dummy shots.
Questions still linger about why such an effect was seen. Still, the results led Merck to put a halt on the studies on Sept. 21.
At the time, top officials with the company and with the National Institutes of Health, which had partially funded the research, said that the failure of this vaccine did not necessarily spell disaster for similar efforts.
"In my mind, this doesn't damn anything," Dr. Anthony Fauci, head of National Institute of Allergy and Infectious Diseases, told The Associated Press in November. "It tells you you need to be very careful with every aspect [of vaccine design and testing]."
But now, some AIDS researchers say that the failure of the vaccine should shape the way these vaccines are studied — a potential change that could affect more than a dozen other potential HIV vaccines that are still being investigated.
"If they are already enrolling patients, they should stop enrolling new patients until a review of the underlying science can be done by an independent outside committee of scientists," van der Horst said. "If they have not started enrolling patients, they should not start and an independent committee of scientists should review the science on which the study was based in light of the new data."
But Dr. Michael Keefer, head of the HIV Vaccine Trials Unit at the University of Rochester Medical Center in Rochester, N.Y., said though the information yielded by the studies was disappointing, it is still useful. And he said research must continue.
"We're at a crossroads now," he said. "We're at a time where we know something for certain, and unfortunately only way to know things for certain is to do these studies in people."
And Keefer, for one, said he does not think the Challenger analogy offered by Gallo is entirely inappropriate.
"I think its similar in that it caused a pause in the program for a period of time, which is reasonable to understand exactly what happened and why," he said. "The result of that, though, is they went back to approach they had taken. They are still flying shuttles, anyway."
Audrey Grayson contributed to this report.