Nearly all Americans will be eligible to get a dose of the, following a decision to expand emergency use authorization for the shots from Moderna and Pfizer-BioNTech to most children as young as 6 months old.
The Food and Drug Administration announced the expanded authorization on Thursday, clearing all recipients of Moderna's COVID-19 vaccine to get a booster dose from the company's newest "bivalent" vaccines — which are tailored to recent Omicron variants — at least two months after their last "monovalent" shot.
But only a portion of the youngest kids who got Pfizer-BioNTech's shots will be eligible to get a shot of their updated COVID vaccine this year.
The FDA had previously greenlighted Pfizer's shots in this age group as a three dose "primary series," after data suggested kids from 6 months old to 4 years old needed a third kid-sized dose to get protection on par with adults after two doses.
Now the FDA says only kids who have yet to complete their third dose can swap out the last shot for an updated vaccine. Early adopters who already completed their third shot some several months ago must wait until the FDA receives more data next year.
"The data to support giving an updated bivalent booster dose for these children are expected in January. The agency is committed to evaluating those data as quickly as possible," the FDA said in a statement.
The agency said it expects children in this age group will still have "protection against the most serious outcomes" from current variants.
"At this time, we do not have clinical data in this age group for a fourth (booster) dose of the original vaccine following the third primary series dose, and thus we cannot yet extrapolate," Pfizer spokesperson Julia Michelle Cohen said in an email.
The Centers for Disease Control and Prevention announced Friday that it had also signed off on updated recommendations to clear the shots for this youngest age group, skipping a meeting of its outside vaccine advisers to weigh the expanded eligibility.
The federal Vaccines.gov portal is expected to be updated Friday to allow parents to search for the new shots formulated for this youngest age group.
Jurisdictions wrapped up placing pre-orders this week for the updated bivalent shots for the youngest children earlier this week, according to planning documents published by the CDC. "There will be a sufficient but finite supply" of the shots available, the agency said.
Only a small fraction of the updated COVID-19 vaccines the Biden administration purchased from Pfizer and Moderna have been used up to date.
Less than 15% of Americans ages 5 and older, the ages previously eligible to get an updated booster, have gotten one so far. Less than a third of seniors — the most vulnerable age group — have gotten the new shot, which in September.
Among children under 5 years old, less than 5% have completed their primary series of COVID vaccination.
"I think the uptake has been woefully slow," the CDC's Barbara Mahon, head of the agency's proposed Coronavirus and Other Respiratory Viruses Division, said at a meeting on Wednesday.
More changes could be on the way soon, Mahon said.
American health authorities have previously floated plans to switch all COVID-19 vaccines to the bivalent formulation, as regulators Europe recently decided to allow. CDC officials have said that the change will become necessary as much of the U.S. stock of monovalent vaccine is due to expire.
"We're also anticipating several upcoming policy discussions around boosters and use of bivalent vaccines in children under 5 years of age, and regarding transition of the primary series from monovalent to bivalent COVID 19 vaccines," said Mahon.