New omicron variants are again driving hospital admissions and deaths higher in recent weeks, causing states and cities to rethink their responses to COVID-19 and the White House to step up efforts to alert the public. Some experts say the warnings are too little, too late. The highly transmissible variants have shown a remarkable ability to get around the protection offered by infection and vaccination. And protection from vaccination is waning for Americans overdue for booster shots. Less than half of all eligible U.S. adults have gotten a single booster shot, and only about 1 in 4 Americans age 50 and older who are eligible for a second booster have received one.