Experts warn that another coronavirus wave may be imminent in the United States, fueled by a more contagious Omicron subvariant that is spreading rapidly in Europe, though they said the trend was more a cause for caution than alarm. The Omicron variant this month began its second sweep through Europe, where past virus surges have been a harbinger of what was to come in the US. Although many countries thought they were free of the worst of Covid and raced to lift restrictions in February and March, the experts are of the view that a highly transmissible Omicron subvariant, BA.2, is contributing to the new surge.