WASHINGTON – Nearly half of high school students say they’ve had sex, yet progress has stalled in getting them to use condoms to protect against the AIDS virus, government researchers reported Tuesday.

Today, four of every 10 new HIV infections occur in people younger than 30, according to the national Centers for Disease Control and Prevention – and the teen years, just as many youths become sexually active, are key for getting across the safe-sex message.

Using a long-standing survey of high school students’ health, the CDC tracked how teen sexual behavior has changed over 20 years. The results are decidedly mixed.