The new study is the first to show that AZT may benefit infected individuals with between 500 and 750 CD4 cells. AZT cut in half the rate at which the CD4 cell count fell below 350. It also appeared to decrease the rate at which early HIV symptoms, such as yeast infections in the mouth, develop. Previous studies have shown that AZT benefits those who are further along in the disease-with CD4 counts of 500 or lower.

The participants included 436 individuals with between 500 and 750 CD4 cells at the beginning of the study. In this group, 9% of those receiving AZT worsened to a level of 350 CD4 cells or lower or developed early HIV symptoms, compared to 18% of those treated with the placebo, the Wellcome Foundation said. Four times as many patients progressed to the level of 350 CD4 cells than developed HIV symptoms.

An additional 211 participants began with between 400 and 500 CD4 cells. In this group, 20% of those receiving AZT worsened to 350 CD4 cells or fewer or developed early HIV symptoms, compared to 38% of those treated with the placebo. No significant differences were found for those who began the study with more than 750 CD4 cells.