By Michael Erman and Bhanvi Satija (Reuters) -About one-in-three COVID-19 cases in the United States are now caused by the BA.2 Omicron sub-variant of the coronavirus, according to government data on Tuesday that also showed overall infections still declining from January’s record highs. Despite the rise of the extremely contagious sub-variant also seen in other countries, U.S. health experts say a major wave of new infections here appears unlikely. U.S. COVID-19 infections have receded sharply since January, although a resurgence in parts of Asia and Europe have raised concerns that one will …