HIV prevalence has fallen 25 percent or more among young people in 15 countries most affected by the epidemic, UNAIDS announced this week - a shift attributed to aggressive HIV prevention campaigns.

"Young people are taking the lead, which is progress," said UNAIDS Executive Director Michel Sidibe. "For the first time there is a correlation between [declining prevalence] and behavior, which for me is very important news in terms of dealing with the epidemic."

The biggest drop was in Kenya, where there was a 60 percent reduction among 15- to 24-year olds between 2000 and 2005. HIV prevalence in urban areas dropped from 14.2 percent to 5.4 percent in this population, and from 9.2 percent to 3.6 percent in rural areas.

UNAIDS links the drop in HIV prevalence to dramatic shifts in sexual behavior among youths. In 13 countries, young people said they were waiting longer before becoming sexually active and were having fewer sexual partners. In addition, they were more likely to use a condom during their most recent sex act.

"Young people have shown that they can be change agents in the prevention revolution," the report concludes.

Analyses in the report are based on the results of population-based surveys and surveys of HIV prevalence among pregnant women. While mathematical modeling suggests that trends in HIV prevalence among young pregnant women mirror trends among all men and women in the same age group, population surveys are more accurate in estimating HIV prevalence.