A California community that has been a bellwether of the coronavirus pandemic’s rampage across the United States warned on Thursday that the number of cases of more contagious COVID-19 variants is increasing to worrisome levels.

“The region’s progress in curbing the pandemic remains precarious,” the health department in Santa Clara County, home to California’s Silicon Valley, said.

“County residents are therefore urged to avoid travel, quarantine if travelling, and consistently use face coverings.”

The situation in Santa Clara, which was home to an early surge of coronavirus in California last year and the nation’s first death from COVID-19, offers a window into the pandemic’s progress across the wider United States.