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Covid booster shot bolsters protection in 5-to-11-year-olds, Pfizer and BioNTech say

Mason Lawrence, 9, gives a thumbs-up after receiving the coronavirus vaccine in New York in November 2021. Pfizer and BioNTech announced they would file for a booster shot for children in this age group. (Michael M. Santiago/Getty Images)

A booster shot of the Pfizer-BioNTech vaccine increases immune defenses against the coronavirus in school-aged children, particularly against the omicron variant, the companies announced Thursday.

Pfizer and BioNTech say they intend in coming days to request authorization from the Food and Drug Administration for a booster for 5-to-11-year-olds. The additional shot was given six months after children were fully vaccinated.

Many scientists have said they think the coronavirus vaccine is a three-dose regimen, but it is unclear whether families will embrace more shots. Uptake of the first shots has been slow, even though the vaccine became available to school-aged children right before the disruptive omicron surge. According to data from the Centers for Disease Control and Prevention, only 28 percent of children in this age group are fully vaccinated.

Meanwhile, studies of real-world vaccine performance found the two-shot regimen from Pfizer and BioNTech, the only vaccine available for children in this age group, provided poor protection against infections during the omicron surge, even compared with the shot’s performance in older adolescents.

The BA.2 “stealth” omicron variant is expected to soon become the dominant strain. Here is what you need to know about a possible new wave of infections. (Video: Brian Monroe, John Farrell/The Washington Post)

The vaccine has been available for 5-to-11-year-olds since November, just before the omicron variant emerged. A CDC study found the vaccine was 46 percent effective at preventing visits to emergency departments or urgent-care clinics in school-aged children. A study from New York state that tracked infections and hospitalizations during December and January found that protection against hospitalization declined from 100 percent to 48 percent — markedly less protective than for teens.

The new data, presented in a news release, supports the idea that a third dose of the vaccine plays a crucial role — and does more than just increase the levels of virus-blocking antibodies.

Studies in adults show that while a third shot increases the level of antibodies, it also hones those antibodies’ ability to block an array of variants — a process called “affinity maturation.”

The data on a booster in 5-to-11-year-olds has not been published or peer-reviewed, but it echoes those findings. Like other booster trials, this study did not measure the ability of the vaccine to stop people from becoming ill but was based on laboratory measurements of the booster’s ability to increase antibodies in their blood.

A month after a third shot, antibodies capable of blocking the original version of the virus were six times higher than they were a month after the second shot among 140 children whose blood was tested. But the booster triggered a bigger, 36-fold increase in antibodies that neutralize the omicron variant. Those tests were run in a smaller group of 30 children.

School-aged children receive a lower dose of the vaccine — a third of what older adolescents and adults get — and some experts have debated whether a higher dose is needed.

The new data “reinforce the potential function of a third dose of the vaccine in maintaining high levels of protection against the virus in this age group,” the companies said in a statement. They added that the dose was “carefully selected based on safety, tolerability and immunogenicity data.”

The data on boosters for children older than 5 is likely to be frustrating to parents and pediatricians who are impatiently awaiting the opportunity to give children younger than 5 a first shot. No vaccines are available to that age group, and results from Pfizer’s ongoing test of a vaccine in children as young as 6 months old are expected in “coming weeks,” according to the company.

Pfizer and BioNTech added a third shot to their vaccine trial for children younger than 5 after the two-shot series failed to muster a sufficiently robust immune response in those children.

Last month, biotechnology company Moderna reported that its pediatric vaccine triggered immune defenses in children as young as 6 months old equivalent to the response that protected adults against the original version. But the Moderna shot provided only minimal protection against infection during the omicron surge. Moderna is expected to submit that data to regulators soon.