The United States is in the throes of another covid-19 uptick, cementing a pattern of the virus surging around the holidays as doctors and public health officials brace for greater transmission after Americans return to school and work this week. Coronavirus samples detected in wastewater, the best metric for estimating community viral activity, suggests infections could be as rampant as they were last winter. A smattering of health facilities around the country, including every one in Los Angeles County, are requiring masks again. JN.1, the new dominant variant, appears to be especially adept at infecting those who have been vaccinated...