Drugmaker Pfizer said it has doses ready to ship and can deliver up to 15 million shots by the end of next week.
The United States has authorised booster doses of the COVID-19 vaccines that target the most common Omicron strain, and shots could be available within days.
The move by the Food and Drug Administration (FDA) on Wednesday tweaks the recipe of shots made by Pfizer and Moderna. Officials hope the modified boosters will blunt yet another winter surge.
“You’ll see me at the front of the line,” FDA vaccine chief Dr Peter Marks told The Associated Press shortly before his agency cleared the new doses.
Until now, COVID-19 vaccines have targeted the original coronavirus strain, even as wildly different mutants emerged. The new US boosters are combination, or “bivalent”, shots. They contain half that original vaccine recipe and half protection against the newest Omicron versions, called BA.4 and BA.5, which are considered the most contagious yet.
The combination aims to increase cross-protection against multiple variants.
“It really provides the broadest opportunity for protection,” Pfizer vaccine chief Annaliesa Anderson told the AP.
As a single dose, Moderna’s vaccine is authorised for those aged 18 and above, while Pfizer’s bivalent candidate is for those aged 12 and above.
The US government has purchased 175 million doses of the booster shots from the two companies in an effort to stave off the worst effects of a potential surge in new infections as schools reconvene and people spend more time indoors as the weather grows colder. Pfizer said it could ship up to 15 million of those doses by September 9.
The FDA in June asked vaccine makers to tailor shots to the two subvariants responsible for the most recent surge in infections worldwide. The BA.5 subvariant currently accounts for more than 88 percent of US infections.
The updated boosters are only for people who have already had their primary vaccinations, using the original vaccines, and they are not to be used for initial vaccinations.
There is one more step before the next booster campaign begins: The Centers for Disease Control and Prevention (CDC) must recommend who should get the additional shot. An influential CDC advisory panel will debate the evidence Thursday — including whether people at high risk for COVID-19 should go first.
“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,” FDA Commissioner Dr Robert Califf said in a statement.
A major concern now is whether people weary of vaccinations will roll up their sleeves again. Just half of vaccinated Americans got the first recommended booster dose, and only a third of those 50 and older who were urged to get a second booster did so.
University of Pennsylvania immunologist E John Wherry said it is time for US authorities to better explain that the public should expect an updated COVID-19 vaccination every so often, just like getting a fall flu shot or a tetanus booster after stepping on a rusty nail.
“We need to rebrand it in a societally normal-looking way,” rather than having a panicked response to new mutants, Wherry said, urging authorities to “give a clear, forward-looking set of expectations”.