A variant of the coronavirus first discovered in the United Kingdom and believed to be more transmissible is present in Chicago, city health officials announced Friday.

California on Wednesday announced the nation’s second confirmed case of the new and apparently more contagious variant of the coronavirus, offering a strong indication that the infection is spreading more widely in the United States.

The first reported U.S. case of the COVID-19 variant that’s been seen in the United Kingdom has been discovered in Colorado, Gov. Jared Polis announced Tuesday, adding urgency to efforts to vaccinate Americans.

Reports from Britain and South Africa of new coronavirus strains that seem to spread more easily are causing alarm, but virus experts say it’s unclear if that’s the case or whether they pose any concern for vaccines or cause more severe disease.