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Pfizer and BioNTech plan to ask the Food and Drug Administration to clear a third dose of their COVID-19 vaccine for children as young as five, the companies announced Wednesday, citing trial results showing a “robust response” of antibodies in this age group after the booster shot. 

In the trial, 140 children ages 5 to 11 years old were given a third dose of the Pfizer-BioNTech COVID-19 vaccine six months after receiving their second shot. Blood drawn from the children showed a six-fold increase in antibodies compared to the amount seen one month after the second dose, indicating “a strong immune response in this age group,” the companies said.

A subset of antibodies from the children in the trial were also tested against the Omicron variant. Those 30 samples had a strong enough antibody response to neutralize the variant, with a “robust response” regardless of whether the children had previously survived a case of COVID-19, the companies said.

“Pfizer and BioNTech plan to submit a request for Emergency Use Authorization (EUA) of a booster dose for children ages 5 through 11 in the U.S. in the coming days,” the companies said in a release. 

While vaccine effectiveness against hospitalization remained relatively high during the Omicron wave, the risk of breakthrough infections among Americans who had received only two doses of a COVID-19 vaccine soared among all age groups – including children. 

According to data presented last week by a Centers for Disease Control and Prevention official, two doses were as little as 24% effective at curbing infection in children 5 to 11 years old during the Omicron wave.

If Pfizer and BioNTech’s request is greenlighted by the FDA and approved by the CDC, only a small handful of children would likely initially be eligible for the booster. According to the CDC, just 28% of Americans ages 5 to 11 have been fully vaccinated since the agency formally recommended the shots for that age group in early November

Federal officials have openly expressed frustration with the lagging pace of vaccinations. The CDC found in March that around 4 in10 parents of children ages 5 to 11 probably would not have their kids vaccinated.

However, the announcement also comes as concerns are mounting among some health experts and officials of a new wave of cases in the coming months driven by the BA.2 subvariant of Omicron. The nationwide pace of COVID-19 cases and hospitalizations has begun to accelerate in recent weeks, with the largest upticks in the Northeast regions, where the subvariant first became dominant. 

“All that stuff you hear about, don’t worry about kids, let them get infected, is a bunch of nonsense. There have been about 12 million cases in kids, there have been over 120,000 hospitalizations,” Dr. Anthony Fauci said Monday, in a lecture at Uniformed Services University.

“We really need to put that myth to sleep that we don’t need to protect the children now,” Fauci added. 

No data for children under five 

The release does not include widely-anticipated data on the immune response in children under five. The FDA in February postponed plans to weigh authorizing two doses for kids in that age group, pledging to return to the issue after the companies submitted data on the subject. 

“We at FDA really understand the urgency that people feel about wanting to get the youngest children vaccinated. We also understand that this is the age range when people are most concerned about potential side effects and the potential safety of vaccines,” Dr. Peter Marks, the FDA’s top vaccines official, told reporters last month

A spokesperson for Pfizer did not respond to a request for comment on when data for three doses in children under five was expected to be released.

“FDA has a lot of familiarity with these data sets and so they could act quickly on them. Assuming the data comes out in April, as is expected, I think the agency could potentially act in May,” former FDA Commissioner Dr. Scott Gottlieb, who sits on Pfizer’s board of directors, told “Face the Nation” on Sunday

Moderna has also released “positive interim data” from trials of just two doses of its vaccine in children as young as six months, with plans to seek the FDA’s authorization in the coming weeks. 

“My hunch is it will slip a little bit because that sense of urgency will have dissipated because infection levels will be relatively low as we get into the spring,” added Gottlieb.