The Biden administration’s planned fall COVID-19 booster campaign cleared a key regulatory hurdle, after the Food and Drug Administration announced Wednesday it has authorized updated shots adapted for the Omicron variant of the virus for Americans as young as 12 years old. 

People could get the new booster as little as 2 months after their last shot of a COVID-19 vaccine. Moderna’s new shots are authorized for Americans as young as 18. Pfizer and BioNTech’s can be given down to age 12.

Boosters from the original formulation are no longer authorized for use in Americans who are eligible to get the new booster shots. 

“As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants,” said Dr. Robert Califf, the FDA commissioner, in a release.

The decision means shipments of the new doses from Pfizer-BioNTech and Moderna can now begin. Many state and local health departments already placed pre-orders last month for the first waves of deliveries.

A Pfizer spokesperson says the company can ship up to 15 million doses of the new vaccine by the end of next week, pending “final quality control checks.”

However, as with previous COVID-19 vaccine rollouts, vaccinators will need to wait for the Centers for Disease Control and Prevention’s own recommendation before administering their first shots from the new vials. That green light is expected by the end of this week, following a two-day meeting of the agency’s outside vaccine advisers this Thursday and Friday.

Pfizer plans to submit a request to the FDA “in early October” for giving the new booster to children down to 5 years old, the company said in a release, and is also working on a submission for boosting kids as young as 6 months old.

The new formulations mark the first significant change to the COVID-19 vaccines since they were rolled out earlier in the pandemic. 

The vials of the so-called “bivalent” shots from each company blend together a component from their original “prototype” shots with another designed to target the Omicron subvariants BA.4 and BA.5 — the strains which are now prevalent across the country. 

“As we head into the fall and winter season, with the potential for greater SARS-CoV-2 spread in schools and at  work, it is important to stay up to date with vaccines as a first line of defense against COVID-19 illness,” Pfizer’s CEO Albert Bourla said in a statement.

Why are the booster shots being changed?

The decision to tweak the design of the COVID-19 vaccines to target these strains stems from meetings of the FDA’s outside vaccine advisers back in June and April earlier this year to weigh the issue, ahead of the months-long ramp-up required for manufacturers to redirect their vaccine factories.

At the time, a majority of the committee’s members favored an approach not far off from the one proposed by Pfizer and BioNTech to accelerate the authorization of new shots that might boost their effectiveness ahead of another feared deadly winter wave of the virus.

The FDA ultimately said it would not require lengthy clinical trials of the shots aimed at BA.4 and BA.5 in humans before authorizing the new booster supply from Moderna as well as Pfizer and BioNTech. 

Instead, the authorization would rely largely on trial data collected from testing the safety and immune response triggered by the new shots in animals, as well as data from other formulations previously trialed by the vaccine makers.

“In the midst of a pandemic, if you wait for all that data to come in, you’ve missed the boat. And so you have to be preemptive,” FDA Commissioner Dr. Robert Califf said on the “Public Health On Call” podcast on Tuesday.

Califf compared the authorization to the regulator’s approach to updating the annual flu vaccine, citing “the totality of the evidence” backing their decision.

In a separate interview this week, CDC Director Dr. Rochelle Walensky hinted that she was also leaning towards signing off on the new shots.

She pointed to her agency’s estimates, which show the BA.4 and BA.5 subvariants and their descendants making up virtually all new infections across the country right now.

“The strategy now is to tailor vaccine for giving us the largest breadth of response, ideally one that would have less waning over time,” Walensky told the “Conversations on Health Care” radio program.

However, even with the authorization in hand, the two vaccine makers say they are still planning to complete human clinical trials of these new shots. 

Federal health officials say they asked for these trials to track the vaccine’s ability to curb future virus variants later this year, which might look very different from the BA.4 and BA.5 strains circulating now. 

Rolling out bivalent booster shots

The push for new fall booster shots will not be without its hurdles for state and local health departments, which are now also juggling annual flu shots and a monkeypox vaccine rollout. 

Twenty million doses were made available for vaccinators to pre-order, from states to pharmacies, according to a spokesperson for the Department of Health and Human Services. All 50 states and the District of Columbia have requested shots.

Planning documents published by the CDC last month urged state and local health departments to prepare to distribute the early shipments to providers that can vaccinate “those at highest risk for severe COVID-19 disease” first, like in nursing homes. 

In a first for the COVID-19 vaccines, part of the supply of new shots the Biden administration purchased from Pfizer and BioNTech are expected to come in single-dose vials. Approved by the FDA last month, these vials could dramatically cut down on wasted doses and make it easier for providers to offer the shots. 

However, the initial tranche of bivalent shots from Pfizer are expected to be far more unwieldy: cartons of 10 vials containing 6 doses each, shipped in minimum orders of 300 doses. Moderna’s vaccine will come in minimum orders of 100 doses. 

The new booster campaign could also make it harder for unvaccinated Americans to find primary series shots, which will still require the original formula. The U.S. is currently averaging less than 40,000 first doses a day, according to CDC figures.

Human clinical trial results will be needed before the primary series of shots can be switched, the FDA said earlier this year. 

“It is expected that many COVID-19 vaccination providers will offer bivalent booster doses, but not all providers are expected to continue carrying primary series COVID-19 vaccines,” the CDC said in its planning guide.