Burton said Moderna and other vaccine companies are testing existing COVID-19 vaccines to determine how effective they are against the omicron variant.

“If we need to manufacture an omicron-specific variant, it’s going to take some weeks, two to three months is probably what we’re looking at to be able to really begin to manufacture,” Burton told ABC.

Noting that the new variant, like earlier ones, sprang up overseas in areas with lower vaccination rates, Biden said it was both a moral imperative and in America’s self-interest to speed up global vaccinations. He noted that the U.S. has already donated more than 275 million doses — more than the rest of the world combined — and is on pace to deliver more than 1.1 billion doses globally by September 2022.

“Now we need the rest of the world to step up as well,” Biden said. “We can’t let up until the world is vaccinated.”

As the holiday season got underway, Biden tried to reassure shoppers that his administration was working to ease supply chain problems. Businesses are working to overcome lingering effects of COVID-related shutdowns and now issues arising from the strong recovery that has generated more demand than many ports, manufacturers and retailers can handle.

The president spoke Monday with the CEOs of Best Buy, Food Lion, Samsung, Etsy and Walmart, among companies. The corporate leaders reassured Biden.

“While we’re all concerned about the supply chain, we have more inventory than we did a year ago, and we have the inventory that we need to be able to support the business,” said Walmart CEO Doug McMillon. “And we are seeing progress. The port and transit delays are improving.”