WASHINGTON, Dec 12 (Reuters) - Three doses of a COVID-19 vaccine is the "optimal care" but two doses of the Pfizer/BioNTech or Moderna vaccines or one of the Johnson & Johnson vaccine remains the U.S. government"s official definition of fully vaccinated, top U.S. infectious disease expert Anthony Fauci said on Sunday. Health officials will continue to evaluate what should constitute the official designation, Fauci, who is the director of the National Institute of Allergy and Infectious Diseases and President Joe Biden"s Chief Medical Advisor, said on ABC"s "This Week With George Stephanopoulos". "Well, I certainly think, George, it"s the optimal care," Fauci said in response to being asked whether three vaccine doses could be the new standard of care. "I mean, for official requirements, it"s still two shots of the mRNA (Pfizer/BioNTech or Moderna) and one shot of the J&J for the official determination of what"s required or not. But I think if you look at the data, the more and more it becomes clear that if you want to be optimally protected you really should get a booster," he added. It will take months to tell whether annual booster doses of the vaccine are needed, Fauci said, adding that he is hoping from an immunological standpoint that one booster dose will be enough to provide protection greater than just the six months offered by the initial vaccine.