SACRAMENTO, Calif. (AP) — The highly contagious omicron variant is evident in 50% to 70% of new coronavirus cases in parts of the most populous state heading into the holidays, California health officials said Thursday.

Omicron has quickly become the most common form of the coronavirus in the U.S., accounting for 73% of all cases, federal officials said in the latest nationwide estimate Monday. The U.S. recorded its first confirmed omicron infection just three weeks ago in a San Francisco resident who had recently traveled to South Africa.

It is now being “detected at increasing proportions in wastewater in multiple regions throughout California,” the California Department of Public Health said.

At least three of the state's health systems have reported that about 50% to 70% of their coronavirus cases are consistent with omicron, the department said without naming the systems.

It cautioned that full genomic sequencing of virus samples is pending and takes several days, but said the early California results track the nationwide estimate.

“Overall, clinical and wastewater data indicate that omicron cases are present in most regions of the state,” officials said.

Gov. Gavin Newsom said Wednesday that California is better positioned to handle the surge than it was a year ago, when serious cases strained hospitals and morgues to the breaking point, and is less affected so far than many other states.

Much about the omicron coronavirus variant remains unknown, including whether it causes more or less severe illness. But Britain’s public health agency said Thursday that early data suggest that people with the omicron variant are between 50% and 70% less likely to need hospitalization than those with the delta strain.

Local officials were also sounding the alarm about the new variant's rapid spread.

Cases in San Francisco are rising three times faster than during the summer delta-fueled surge, the San Francisco Department of Public Health said Thursday. Though the variant may generally result in less serious illness than delta, officials warned that “transmission is so much higher that San Francisco is likely to see high rates of hospitalizations in the coming weeks."

Los Angeles County, the nation’s most populous, reported more than 6,500 new cases on Wednesday. That figure is double the number of cases from Tuesday, and by Thursday there were 8,633 new cases. Health officials were concerned that could climb to more than 20,000 cases a day by the end of the year.

Barbara Ferrer, the county’s public health director, said the doubled cases represents “one of the steepest rises we’ve ever seen over the course of the pandemic.”

“These numbers make it crystal clear that we’re headed into a very challenging time over the holiday,” she said. “If our case numbers continue to increase at a rapid pace over this week and next, we could be looking at case numbers we have never seen before.”

Orange County had more than 650 positive tests reported Thursday compared with about 400 on a given day last week, and Dr. Regina Chinsio-Kwong, the county’s deputy health officer attributed most of the increase to omicron.

A workplace holiday party with about 50 people in Davis, west of Sacramento, led to an outbreak of at least 16 cases, at least 10 of whom were identified as having omicron, Yolo County officials said. All 16 were fully vaccinated and eight had received their booster. 

Public health officials similarly said at least 28 vaccinated people tested positive after a holiday party in Marin County, north of San Francisco, and they believe it involves the omicron variant.

Scientists say omicron spreads even easier than other coronavirus strains, including delta. Early studies suggest the vaccinated will need a booster shot for the best chance at preventing an omicron infection but even without the extra dose, vaccination still should offer strong protection against severe illness and death.

Newsom held out that hope as he urged people to get vaccinated or their booster shots.

“We’re all exhausted by this,” he acknowledged. “But we have something we never had in the past, and that’s the power of these life-saving vaccines and the power to get boosted to get through this arguably fifth wave of this pandemic.”