Nearly all teenagers needing intensive care for covid-19 were unvaccinated in a study of more than 1,000 hospital patients in the United States.

The Pfizer-BioNTech coronavirus vaccine prevented 94 percent of hospitalizations and was 98 percent effective at keeping patients out of intensive care (ICU) or from requiring life support, per the peer-reviewed analysis published Wednesday in the New England Journal of Medicine.

As pediatric hospitalizations surge in many parts of the United States, fueled by the more transmissible omicron variant, the study’s findings help illustrate how vaccination can protect young people from severe complications and death.

“Nearly all hospitalizations and deaths in this population could have been prevented by vaccination,” writes Kathryn M. Edwards, scientific director of the Vanderbilt Vaccine Research Program, in an editorial to the journal about the study, which was conducted by experts from pediatric hospitals in collaboration with researchers from the U.S. Centers for Disease Control and Prevention.

About 36 percent of children between 12 and 17 have not received any dose of a vaccine, according to the CDC. That’s months after the Food and Drug Administration authorized the Pfizer-BioNTech coronavirus vaccine in May for those between 12 and 15. The CDC has since also recommended that children between 12 and 17 get a booster dose.

And although it remains true that children who contract the coronavirus are far less likely than adults to get seriously sick or die of it, public health officials have encouraged children ages 5 and older to get vaccinated.

Coronavirus cases spiked globally in the first weeks of 2022, despite record-high vaccination rates. Here’s how the omicron variant took off. (Jackie Lay, John Farrell/The Washington Post)

The study examined data from 1,222 patients between 12 and 18 years old who were hospitalized between June 1 and Oct. 25, 2021, in one of 31 hospitals across the United States taking part in the Overcoming Covid-19 study, a research collaboration between pediatric hospitals and the CDC. The study included 445 teens who were hospitalized for covid-19 and 777 who were hospitalized for other reasons.

Of the 1,222 patients, 299 were fully vaccinated — a number Vanderbilt’s Edwards called “distressing” in her editorial.

“Although these rates have increased somewhat since the data in this study were compiled, as of December 1, 2021, only 60% of U.S. adolescents had received a single dose of a Covid-19 vaccine, and only 50% had been fully vaccinated,” she writes. “Vigorous efforts must be expended to improve vaccination coverage among all children and especially among those at highest risk for severe covid-19.”

Forty percent of the patients with a positive coronavirus rest result were admitted to the ICU. All but two were unvaccinated. And all but one of those who required life-supporting interventions, such as being put on a ventilator, were unvaccinated.

The hospitals included in the study were in cities, and more than half of the patients with covid were hospitalized in Southern states, where the delta variant of the coronavirus was spreading especially quickly during the study period.

Even with those limitations, the study is particularly valuable, because its subjects are more diverse and in poorer health than those who are typically enrolled in the kinds of trials that pave the way for authorizing new treatments like the coronavirus vaccines, notes Manish M. Patel, one of the study authors and a member of the CDC’s covid-19 Response Team. It shows that the vaccines are effective at preventing severe covid-19 even in the most vulnerable young people.

“It really takes the introduction of a vaccine in the real world to understand whether the vaccines work in the real world,” Patel adds.

About a quarter of the patients in the study were Black, and a quarter were Hispanic. About three-fourths of the teens in hospital in both the control and the case groups had at least one preexisting condition, including obesity, diabetes or asthma. And the patients with a positive coronavirus test were more likely to live in areas deemed more “socially vulnerable” than their peers in the control groups.

“When you see something work that well in such a sick population … that’s very reassuring that it’s definitely been working much better in the general population,” Patel said of the vaccine, “although you can’t get much higher than 94 percent.”