Nationwide sex education campaigns have been credited with a massive drop in the number of teenagers who are sexually active.

Soul City, which runs the Soul Buddyz campaign, welcomed new reports of a 3% drop in the number of teenagers who have had sex.

The Medical Research Council's youth risk behaviour survey revealed that the number of teenagers between Grades 8 and 11 having sex declined from 41% in 2002 to 38% in 2008. The survey's results were released on Tuesday.

Of the 10270 children surveyed, about 19% had had sex in the three months prior to the survey, compared to 28% in 2002.

Research director Priscilla Reddy said the decrease in sexual activity was due to "so many millions of rands of intervention in the area of sexual behaviour".

"Loads of money has been poured into HIV and Aids prevention," she said.

Sue Goldstein, senior executive for Soul City, said: "I'm gratified. Maybe our interventions are actually beginning to work."

She said the Soul Buddyz message was: "Don't have sex until you're really ready, and be sure that you're able to have safe sex."

Joan van Niekerk, manager of training and advocacy for Childline SA, said: "The reduction in sexual behaviour is a promising outcome because we know that the later children make their sexual debut, the less they risk infection by HIV."

Linked to the decrease in sexual behaviour by teenagers was the number of children who reported having had a sexually transmitted disease, down from 7% in 2002 to 4% in 2008.