When AIDS researchers released results last month from a six-year trial in Thailand of a new AIDS vaccine, they said it showed some promise for new avenues of research, though they freely admitted their data was weak.

Now two published accounts citing anonymous AIDS researchers who were given confidential briefings about the trial results have reported that the data, released on Sept. 24, may be even weaker than the authors admitted  essentially, instead of being 31 percent better than nothing, the vaccine might be only 26 percent better.

The accounts were on Science magazine’s Web site and in The Wall Street Journal.

The debate is over which participants in the study should be counted  all 16,395 Thais who participated at some point or only the ones who got all the doses of the vaccine and stayed in the study for the full time.

The researchers said last month that the vaccine seemed to work 31 percent better than a placebo  and there was only a 4 percent chance that that 31 percent difference was simply a fluke. To some it seemed that a promising step had been made in the long search for a vaccine against AIDS, which has killed more than 25 million people.