The Omicron variant of Covid-19, which had been undetected in the US before the middle of this week, had been discovered in at least five states by the end of Thursday.
Just a day after the first known US case was found in California, tests showed the variant had infected at least five people in the New York City metropolitan area plus a man from Minnesota who had attended an anime convention in Manhattan in late November.
A Colorado woman who had recently travelled to southern Africa, a Hawaii resident with no recent travel history and another California resident who travelled to South Africa last month also were infected by the variant, officials said.
Much remains unknown about Omicron, including whether it is more contagious, as some health authorities suspect, whether it can thwart vaccines and whether it makes people as sick as the original strain.
Health officials in each state said there was no cause for undue alarm. But the spread of the cases, some involving people who had not been away from home recently, meant the variant was likely already circulating domestically in some parts of the country.
“We gotta assume there’s a lot more behind that and that it has been here for a meaningful amount of time,” New York City Mayor Bill de Blasio said at a news conference with Governor Kathy Hochul.