Americans who got the updated COVID-19 booster shots are better protected against symptomatic infection than those who haven’t - at least for now, U.S. health officials said Tuesday.

Updated boosters rolled out by Pfizer and rival Moderna in September have been a hard sell for vaccine-weary Americans. Only about 13% of U.S. adults so far have gotten a “bivalent” shot that targets the Omicron strain as well as the original coronavirus. On Tuesday, White House officials announced a renewed push for more Americans to get the latest shots.

In the first look at the new shots' real-world effectiveness, the Centers for Disease Control and Prevention tracked people with coronavirus-like symptoms who sought testing at drugstores around the country between September and early November. Researchers compared the vaccination status of those who wound up having COVID-19 with those who didn’t.

The new Omicron-targeting booster added 30% to 56% protection against symptomatic infection, depending on how many prior vaccinations someone had, how long ago and their age, the CDC concluded.

People getting the greatest benefit are those who'd never had a prior booster, just two doses of the original COVID-19 vaccine at least eight months earlier, said CDC's Dr. Ruth Link-Gelles, who led the study.

But even people who got a summertime booster of the original vaccine before seeking the new fall formula were 30% to 40% more protected than if they’d skipped this latest shot, she said.

“We think about it as the additional benefit or incremental benefit of getting one more dose, and in this case that one more dose is a bivalent,” Link-Gelles said.

The updated boosters target the BA.5 Omicron strain that until recently was the most common type. The original COVID-19 vaccines have offered strong protection against severe disease and death no matter the variant, but protection against mild infection has proved temporary. CDC’s analysis tracked only the first few months of the new boosters’ use so it’s too early to know how long the added protection against symptomatic infection lasts.

But “certainly as we enter the holiday season, personally I would want the most possible protection if I’m seeing my parents and grandparents,” Link-Gelles said. “Protection against infection there is going to be really helpful, because you potentially would stop yourself from getting a grandparent or other loved one sick.”

To that end, the Biden administration announced a six-week campaign urging people - especially seniors - to get the boosters, saying the shots could save lives as Americans gather for the holidays.

Even protection against severe illness slipped when BA.5 was dominant, the reason health authorities have strongly urged older adults and others at high risk not to skip the new booster.

Adding to the uncertainty, the coronavirus still is mutating and now relatives of BA.5 are on the rise.

Earlier this fall, Pfizer and Moderna released lab tests showing that getting an updated booster revs up people’s levels of virus-fighting antibodies, including against BA.5. The companies point to preliminary antibody evidence that the new shots may offer at least some protection against the even newer Omicron subtypes as well, despite not being an exact match.