The Pfizer-BioNTech vaccine was 93 percent effective against hospitalization with Covid-19 among 12- to 18-year-olds, the Centers for Disease Control and Prevention reported on Tuesday, the strongest evidence to date of the vaccine’s ability to keep young people out of the hospital.

With federal regulators now considering authorizing the vaccine for children ages 5 to 11, the study offered additional signs that extending vaccines to more young people could not only reduce the spread of the virus in the United States, but also protect those children from the rare cases in which they become severely ill.

“This evaluation demonstrated that two doses of Pfizer-BioNTech vaccine are highly effective at preventing Covid-19 hospitalization among persons aged 12–18 years,” the agency’s scientists wrote, “and reinforces the importance of vaccination to protect U.S. youths against severe Covid-19.”

The agency studied young people who were hospitalized at 19 pediatric hospitals across 16 states from June through September, as the Delta variant spread across the country and exacted a devastating toll in less-vaccinated states in the South and West. It compared the odds of vaccination among children hospitalized with Covid and children hospitalized with other illnesses.

Among the 179 patients in the study who had Covid, three percent were vaccinated and 97 percent were unvaccinated. Twenty-nine of the young Covid patients needed life support, and two died; all of those patients were unvaccinated, the agency said. Vaccinated children with Covid also tended to have shorter hospital stays than unvaccinated children.

Nearly three-quarters of the Covid patients in the study had at least one underlying health condition, including obesity, diabetes, asthma or respiratory disorders, putting them at higher risk of severe illness.

As of Monday, the C.D.C. said, 46 percent of children ages 12 to 15 were fully vaccinated nationwide, as were 54 percent of 16- and 17-year-olds. The Pfizer-BioNTech vaccine is authorized for emergency use in children ages 12 to 15, and fully approved in people ages 16 and over. Booster shots have not been authorized for anyone in the United States under 18 years old.

Pediatric hospitalizations rose as the Delta variant spread across the United States, reaching their highest level during the pandemic in September, the C.D.C. said.

A clinical trial of the Pfizer-BioNTech vaccine had earlier shown that the shots were highly effective at preventing Covid cases in children, but had not examined effectiveness against hospitalization in that group.