WASHINGTON/CHICAGO, Aug 25 (Reuters) – The United States plans to roll out an updated COVID-19 booster vaccine to include Omicron subvariants of the coronavirus. Regulators are reviewing the shots and could give the go-ahead as soon as next week.Here is what you need to know:ARE WE GETTING NEW VACCINES?Pfizer Inc (PFE.N) with partner BioNTech SE (22UAy.DE) and Moderna Inc (MRNA.O) completed applications this week to the U.S. Food and Drug Administration for COVID-19 vaccine boosters retooled to target versions of the Omicron variant of the virus.These so-called bivalent vaccines include both the currently dominant BA.4/BA.5 Omicron subvariants and the original version of the virus.The Pfizer vaccine would be for people aged 12 and older, while Moderna’s would be for those 18 and older.The FDA will likely decide on the vaccine soon. The U.S. Centers for Disease Control and Prevention (CDC) has scheduled a two-day meeting of its expert advisers beginning Sept. 1, a step that typically follows FDA authorization.The United States has ordered 175 million doses from Pfizer/BioNTech and Moderna, which are expected to be ready to ship in September.WHO SHOULD GET AN UPDATED BOOSTER?Government health officials say the boosters are needed because immunity wanes over time and the vaccines help prevent serious disease and death.Several experts said they do not expect the updated vaccines to be game changing and urged public health officials not to overstate their benefits.”What the administration is asking us to do is to accept this bivalent vaccine is significantly better than the current ancestral strain vaccine. It would be nice if there were data to support that,” said Dr. Paul Offit, an infectious disease expert at the University of Pennsylvania and a member of the FDA’s vaccine advisory panel.”Right now, what they’re asking you to do is trust them, and to trust them with mouse data, and I think that’s a lot to ask.”Currently, a fourth shot, or second booster, is restricted largely to people over 50 and those who are immunocompromised or at high risk. The government plans to open the Omicron boosters to people from age 12, according to a CDC document.People in these same risk groups are most likely to benefit from the new boosters, said Dr. Celine Gounder, an infectious disease epidemiologist and an editor-at-large at Kaiser Health News.”If you don’t fall into one of those categories, it’s really a toss up as to how much additional benefit you’re going to get,” she said.Gounder recommends those who have recently gotten a booster or COVID-19 wait at least three months to give the immune system the best chance to mount a robust response.John Moore, a professor of microbiology and immunology at Weill Cornell Medical College in New York, said the most important boost is the first one. “Anyone who has not received that boost should do so as soon as possible, and irrespective of the composition of the vaccine,” he said.WHAT DOES THE DATA SAY?Pfizer has presented data on its BA.4/BA.5 booster from studies in labs and animals. The company says it generated a strong neutralizing antibody response against those and other Omicron variants, as well as the original strain of the virus.The company provided regulators with data from a human trial testing the immune response of a shot that combined the original vaccine with the BA.1 Omicron variant. It plans this month to start a similar trial of the BA.4/BA.5 booster in those aged 12 and older.Moderna’s application to the FDA includes data from animal studies of the BA.4/BA.5 booster. A mid-to-late stage trial for the vaccine in people is underway.