NEW YORK (AP) — The first years of the pandemic saw a huge decline in high school students having sex, according to a government survey.

Teen sex was already becoming less and less common before COVID-19.

About three decades ago, more than half of teens said they’d had sex, according to a large government survey conducted every two years. By 2019, the share was 38 per cent. In 2021, 30 per cent of teens said they had ever had sex. That was the sharpest drop ever recorded by the survey.

The Centers for Disease Control and Prevention on Thursday released reports analyzing the latest findings from the survey that looks into risky youth behaviours, including smoking, drinking, having sex and carrying guns.

More than 17,000 students at 152 public and private high schools responded to the 2021 survey. Participation was voluntary and required parental permission, but responses were anonymous.

The CDC also noted declines in students who said they were currently having sex or who’d had at least four sex partners.

The declines clearly had a lot to do with the pandemic that kept kids isolated at home for long stretches and, often, under extended adult supervision, experts said.

Health officials generally like to see trends that result in fewer teen pregnancies and sexually transmitted infections, but the decline in teen sex coincided with increased reports of social isolation and poor mental health.

“I think these together paint a picture of high school students building fewer strong interpersonal connections that can be protective of good mental health,” said Laura Lindberg, a Rutgers University researcher who studies adolescent sexual behaviour.

“This is an opportunity to say maybe teens are having too little sex,” said Lindberg, who was not involved in the reports.

The CDC’s Kathleen Ethier said the decline may be a good thing if it reflects more young people making healthy decisions to delay sex and reduce their number of partners.

“But what concerns me is this is potentially a reflection of social isolation,” said Ethier, director of the CDC’s division of adolescent and school health.

The 2023 survey, which will show if the decline was temporary, is currently underway.

Another finding: The proportion of high school kids who identify as heterosexual dropped to about 75 per cent, down from about 89 per cent as recently as 2015. Meanwhile, the share who identified as lesbian, gay or bisexual rose to 15 per cent, up from eight per cent in 2015, when the survey began asking about sexual orientation.

There were also increases in the proportion who said “other” or that they were questioning or uncertain, the CDC found. The changes may be at least partly related to social changes that have reduced the stigma about identifying as not heterosexual, Lindberg said.