SACRAMENTO, Calif — California health care workers will be required to have coronavirus booster shots to ensure that hospitals are ready to deal with a surge in cases as the more-transmissible omicron variant spreads throughout the state.

Gov. Gavin Newsom announced the order Tuesday on his personal Twitter account and planned to provide more details at a Wednesday news conference.

California already requires health care workers to be vaccinated against the coronavirus, a directive that took effect in September and has since led to the firing or suspension of thousands of people. Now it will join New Mexico as at least the second state to require booster shots for health care workers.

Last week, Newsom, who imposed the first statewide shutdown order in March 2020, warned that cases would likely rise and re-imposed a rule requiring everyone to wear masks at public indoor gatherings.

Concerns stem from the rise of omicron, which as of Monday was the dominant variant of the coronavirus in the United States. Areas in the Midwest and Northeast are seeing the biggest jump in cases and hospitalizations amid frigid temperatures that have kept people indoors.

Much about the variant remains unknown, including whether it causes more or less severe illness. Scientists say omicron spreads more easily than other coronavirus strains, including delta. Early studies suggest the vaccinated will need a third shot for the best chance at preventing infection but even without the extra dose, vaccination still should offer strong protection against severe illness and death.

California has so far fared far better than many other states. The U.S. Centers for Disease Control and Prevention lists California as a place with “high” transmission of the virus, along with nearly everywhere else in the country. But in the last week California averaged 114 new cases per 100,000 people, less than half the national rate.

While 70% of Californians have been fully vaccinated, that still leaves 30% — or roughly 12 million people — who haven’t been. The California Department of Public Health says people who are not vaccinated are seven times more likely to get infected, nearly 13 times more likely to be hospitalized and nearly 16 times more likely to die from the coronavirus.

Coronavirus related hospitalizations have been rising slowly in California, up 15% in the last 11 days to 3,852. That’s less than half as many as during the late summer peak and one-fifth of a year ago, before vaccines were widely available.

But while hospitals overall have fewer patients than last winter, many have fewer workers to treat the patients they do have. The staffing shortage comes as businesses are having trouble finding workers, including hospitals. A recent study by the University of California-San Francisco estimated the state’s nursing shortage could persist until 2026.