WASHINGTON, Dec 29 (Reuters) - Top U.S. infectious disease adviser Anthony Fauci said on Wednesday that the surge in the COVID-19 Omicron variant in the United States is likely to peak by the end of January. "I would imagine given the size of our country, and the diversity of vaccination versus not vaccination, that it"s likely to be more than a couple of weeks, probably by the end of January," he said on CNBC.