Some school systems around the U.S. have extended their holiday break or switched back to online instruction because of the explosion in COVID-19 cases. Others are pressing ahead with in-person classes amid a seemingly growing sense that Americans will have to learn to co-exist with the virus. School districts in cities such as Milwaukee, New York, Detroit and beyond found themselves in a difficult position at the start of the second half of the academic year because of the super-contagious omicron variant. Many parents want their children back in school, while some teachers fear infection.