• The Centers for Disease Control and Prevention backed Pfizer boosters for kids 12 to 15 years of age.
• The recommendation comes amid an increase in pediatric hospitalizations as omicron infections surge across the U.S.

Children ages 12 to 15 are now eligible for Pfizer and BioNTech's Covid booster shots, giving them an extra dose of protection as they return to school amid an unprecedented surge of infections across the U.S.

The Centers for Disease Control and Prevention on Wednesday recommended the booster shot for younger adolescents at least five months after their second dose.

"It is critical that we protect our children and teens from COVID-19 infection and the complications of severe disease," CDC Director Dr. Rochelle Walensky said in a statement Wednesday evening. "This booster dose will provide optimized protection against COVID-19 and the Omicron variant."

Earlier Wednesday, the CDC's independent committee of vaccine experts voted overwhelmingly in favor of lowering the eligibility age for Pfizer boosters to children who are 12 to 15 years old. The CDC had previously backed the boosters for 16- and 17-year-old teenagers in December.

Hospitalizations of children infected with Covid are rising in the U.S. as the highly contagious omicron variant drives a wave of infection in the broader population. Multiple studies have shown that booster shots significantly increase protection against infection and severe illness.

Dr. Grace Lee, who chairs the committee of vaccine experts, said the pandemic has burdened an entire generation of children whose mental and emotional health has suffered as a consequence of school closures and separation from their peers. 

Lee said vaccination was crucial to preventing transmission of the virus and keeping schools and the broader community open so children can thrive. She said the impact of infection on children's long-term health also remains unclear.

"I also truly believe we have not yet addressed the long term impact of Covid infection in children," Lee said.  "I think we haven't even scratched the surface of what we're going to see."

There are about 3,800 kids hospitalized with Covid as of Wednesday, according to a seven-day average of data from the Department of Health and Human Services, up 64% over the past week and the highest level since HHS started tracking the data in the summer of 2020.

Dr. Sara Oliver, a CDC official, told the committee that hospitalizations among 12- to 15-year-old adolescents has remained relatively stable, though she noted that her data only goes through Dec. 10 and may not reflect new infections from omicron.

Oliver said the effectiveness of boosters in 12- to 15-year-old kids is unknown, but third shots are likely to increase protection. A recent study by the U.K. Health Security Agency found that boosters are up to 75% effective at preventing symptomatic infection. The original two-dose Pfizer vaccine, however, is only about 10% effective at preventing symptomatic infection 20 weeks after the second dose, according to the study.

Dr. Helen Keipp Talbot, the only committee member to vote against the decision, said she supports boosters but believes vaccinating all eligible children with the first two doses should take priority over third shots.

"I don't think it's fair for 12- to 17-year-olds who have been vaccinated to risk myocarditis again for an unknown benefit because their colleagues won't get vaccinated," Talbot said.

The Food and Drug Administration on Monday authorized Pfizer booster shots for kids ages 12 to 15. Dr. Peter Marks, director of the FDA group responsible for vaccine safety, told the CDC panel that the rapid spread of omicron prompted the agency to act fast on boosters for adolescents.

Marks said the FDA did not identify any new safety concerns after evaluating real-world data from Israel on more than 6,000 kids ages 12 through 15 who received Pfizer boosters. Among those kids, there were no new cases of myocarditis or pericarditis, rare side effects where the heart is inflamed or swells.

Dr. Sharon Alroy-Preis, head of public health services in Israel, told the committee there were two cases of myocarditis in the 12 to 15 age group after more than 40,000 booster doses administered.

Myocarditis appears most common after the second Pfizer dose for kids ages 12 to 15. The CDC's vaccine safety team found 265 cases total in adolescents 12 to 15 who received two Pfizer doses through Dec. 19, 2021. The overwhelming majority of the cases, 221, occurred after the second dose and 90% of patients were boys.

Myocarditis resulted in 251 hospitalizations, but 96% of the patients were discharged home. The condition remains rare with 45 cases reported per 1 million second doses administered in boys ages 12 to 15, and 3.8 cases per million second doses among girls in the same age group.

About 47,000 adolescents ages 16 to 17 have received Pfizer booster doses in the U.S., the next age group eligible for boosters, and 95% of reported side effects were not serious, according to the CDC.

Dr. Evelyn Twentyman, a CDC official, told the committee that vaccinations in Israel – where the nation has rolled out a massive booster campaign – showed myocarditis in people ages 16 and older was even more rare following a booster shot.

Dr. Julie Bloom, director of the Texas Children's Hospital Immunization Project, told the committee that a booster recommendation for kids 12 years and older "cannot come soon enough."

Bloom said children 12 and older who are vaccinated with Pfizer are already starting to lose their immunity against Covid since they received their first two doses, putting them at increased risk from omicron.

At least 7.8 million children have caught Covid since the pandemic started, according to the American Academy of Pediatrics. More than 1,000 children have died from the virus, according to data from the Centers for Disease Control and Prevention.

"We must do everything in our power to minimize any further detrimental effects to the mental health, physical well being and education of our children," Bloom said.

White House chief medical advisor Dr. Anthony Fauci, during a news conference Wednesday, said omicron appears less severe for kids than delta, but he cautioned against complacency, urging parents to get their kids vaccinated and boosted when eligible.

 — CNBC's Nate Rattner, Dawn Kopecki and Lauren Feiner contributed to this report