NEW YORK -- Scientists acknowledged that an HIV vaccine recently tested in Thailand may be less effective than they originally suggested, but said it still provided valuable leads for further research.

When first publicly disclosing the outcome of the vaccine trial in September, researchers said the vaccine had lowered the risk of infection by about 31%. That result was modest but statistically significant. Coming after two decades of failed HIV-vaccine trials, the announcement was welcomed by researchers around the world.

But two other analyses of the trial data undercut the significance of that result. The additional analyses were published Tuesday in the New England Journal of Medicine, and were also discussed by researchers attending an AIDS meeting in Paris. Details of the secondary analyses were disclosed in The Wall Street Journal on Oct. 12.

The two additional analyses offer a more nuanced picture, suggesting the vaccine's apparent modest effectiveness against HIV, the virus that causes AIDS, could have been the result of statistical chance. Still, many scientists say the Thai experiment was useful because it was the first large-scale HIV-vaccine trial to yield a positive result.

"The results are qualitatively similar along all three analyses," said Seth Berkley, president and chief executive of the International AIDS Vaccine Initiative, who was at the Paris meeting. "Most of the skeptics would say that there's a signal there" that indicates an immune response.