The Omicron variant of the coronavirus has spread to about one-third of US states, but the Delta version remains the majority of Covid-19 infections as cases rise nationwide, US health officials have said.

Though the emergence of the new variant has caused alarm worldwide, Dr Anthony Fauci, the top US infectious disease official, told CNN “thus far it does not look like there's a great degree of severity to it.”

At least 16 USstates have reported Omicron cases: California, Colorado, Connecticut, Hawaii, Louisiana, Maryland, Massachusetts, Minnesota, Missouri, Nebraska, New Jersey, New York, Pennsylvania, Utah, Washington and Wisconsin, according to a Reuters tally.