Pfizer asked U.S. regulators on Monday to license its COVID-19 vaccine combination that adds protection against newer variants of the coronavirus, marking an important step toward kicking off a booster campaign in the fall. .

The country’s Food and Drug Administration (FDA) ordered vaccine manufacturers to modify their doses so that they protect against the BA.4 and BA.5 variants, which are the ones that best evade the immunity of the vaccinations or previous infections.

If the FDA quickly authorizes combination vaccines made by Pfizer and its partner BioNTech, boosters could be offered in a matter of weeks. The United States has a contract to buy 105 million of the updated doses from Pfizer as soon as health authorities give the go-ahead, and the company said the doses are ready to ship.

Moderna is due to file a similar request soon, and the United States has a contract to buy 66 million doses of its updated vaccine.

“It’s going to be really important that people this fall and winter get the new vaccines. They are designed for the virus out there,” Dr. Ashish Jha, White House COVID-19 response coordinator, said last week.

At least for now, the BA.5 variant is currently responsible for nearly all COVID-19 infections in the United States and much of the world. There is no way of knowing if it will still be a threat this winter or if another variant has replaced it.

The news comes after Britain a week ago became the first country in the world to license a different upgrade to Moderna’s COVID-19 vaccines, shots that add protection against the original omicron that struck last winter.

The United States has opted not to use that earlier modification of the vaccine, setting up a situation one fall in which different countries will use different versions of booster shots to increase protection against another possible winter surge.

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