Researchers in Ohio said Wednesday that they’ve discovered two new variants of the coronavirus that likely originated in the U.S. — one of which quickly became the dominant strain in Columbus, Ohio, over a three-week period in late December and early January.Like the strain first detected in the U.K., the U.S. mutations appear to make Covid-19 more contagious but do not seem like they will diminish the effectiveness of the vaccines, researchers said.The Ohio State University researchers have not yet published their full findings, but said a non-peer-reviewed study is forthcoming. Jason McDonald, a spokesman for …