With the full results of the Thai HIV vaccine trial at a conference in Paris, not only the HIV/AIDS research community, but the world in general, can breathe a sigh of relief: The vaccine candidate does appear to offer a real, albeit modest, level of protection against HIV infection.
After the preliminary results were released late last month, many raised concerns about whether the 31% decrease in HIV infection risk shown by the vaccine candidate was genuine or a statistical anomaly. The doubts were in part fueled by hints of additional analyses that yielded weaker and non-significant effects.
The full data, presented at the meeting and published today in the New England Journal of Medicine (NEJM), alleviated some of those uncertainties by showing the same trend in three different analyses -- the intent to treat (ITT), which included all 16,402 subjects; the modified intent to treat (MITT), which excluded seven individuals who were infected with HIV before the trial even began (and was the only analysis made public last month); and the per protocol analysis, which excluded any subject who did not receive all six doses of the vaccine within the correct time periods (about 25% of subjects) as well as any individuals who became infected over the course of the study (about 31% of subjects).
What's important now, researchers agree, is learning as much as possible from the results of this trial. Two "intriguing" trends in particular that emerged during the meeting deserve a closer look. First, the vaccine seemed to provide a higher level of protection early that waned over time, and second, that protection appeared to be stronger for low and moderate risk groups, as opposed to the high risk group.
Another area that warrants further investigation is the mechanism behind the vaccine's effectiveness. The vaccine is a combination of two HIV vaccine candidates -- one that showed no effect and another that was never tested in an efficacy trial. "The combination of the two worked," a scientist said, "and so the question is why? What's the mechanism?"
During a press conference this morning (20th October 2009), an American Colonel of the Walter Reed Army Institute of Research and the US Military HIV Research Program (MHRP) said
the trial revealed no difference in viral load or CD4 counts of infected individuals, suggesting that "those immune responses that might be able to initially prevent HIV infection and those that modulate [the virus] once you have become infected might be quite different."
Reference: Jef Akst. (20th October 2009 03:20 PM GMT). Modest HIV protection confirmed.- [The Scientist online publication].- <
http://www.the-scientist.com/blog/display/56067/ >.- Screen Display.
