The U.S. has reached an important milestone in the pandemic, according to federal health officials.

Going forward, COVID-19 could be treated more like the flu, with one annual shot offering year-long protection against severe illness for most people.

"Barring any new variant curve balls, for a large majority of Americans we are moving to a point where a single, annual COVID shot should provide a high degree of protection against serious illness all year," said White House COVID response coordinator Ashish Jha at a press briefing Tuesday.

The federal government has started rolling out a new round of boosters for the fall — they are updated versions of the Moderna and Pfizer-BioNTech vaccines targeting both the original coronavirus and the two omicron subvariants that are currently causing most infections.

These vaccines could be tweaked again if new variants become dominant in the future, which is how the flu shot works. Every fall, people get a new flu vaccine designed to protect against whatever strains of the virus are likely to be circulating that season. The hope is the COVID boosters will act the same way.

Jha cautioned that older people and those with health problems that make them more vulnerable to severe disease may need to get boosted more often. But for most people Jha hopes this latest booster will be the last shot they need for at least another year.

Throughout the pandemic, SARS-CoV-2 has been incredibly unpredictable and has been evolving much faster than anyone expected, so officials say they will continue to monitor the virus closely and they are ready to reprogram the vaccines again if necessary.

"You've got to put the wild card of a way-out-of-left-field variant coming in," said White House adviser Dr. Anthony Fauci, at the briefing. If that happens he says the recommendations may change. But, "if we continue to have an evolution sort of drifting along the BA.5 sublineage," he says the annual shot should be able to cover whatever is out there as the dominant variant.

But there is still a lot of debate about just how much of an upgrade the new boosters will really be. Some infectious disease experts are not convinced the updated vaccines will be a game-changer, because they haven't been tested enough to see how well they work.

"I think the risk here is that we are putting all our eggs in one basket," Dr. Celine Gounder, a senior fellow at the Kaiser Family Foundation, told NPR. "We're only focusing on boosting with vaccines. I think the issue is people are looking for a silver bullet. And boosters are not a silver bullet to COVID."

Federal officials are concerned that a low number of people will sign up for the new boosters, following a low demand for the initial booster shots. According to the Centers for Disease Control and prevention only 34% of people over 50 have gotten their second booster.

So, as we head into the winter, the administration is urging everyone age 12 and older to get boosted right away to help protect themselves and the more vulnerable people around them. People have to wait at least two months since their last shot and should wait at least three months since their last infection.

But they can sign up to get a COVID booster at the same time as a flu shot.

Because Congress has balked at providing addition funding to fight the pandemic, the new boosters are likely to be the last COVID shots provided for free. People who have insurance will get them covered through their policies. The administration says it's working to make sure those who are uninsured have access to future COVID-19 vaccinations.