California will require health care workers to get a COVID-19 booster vaccine in an effort to reduce and prevent the spread of the highly transmissible omicron variant, Gov. Gavin Newsom said Tuesday.

Newsom, in a Twitter post, said the state plans to take “immediate actions to protect Californians and ensure our hospitals are prepared.”

State public health officials initially moved in August to require workers in health care settings like hospitals and skilled nursing facilities to get fully vaccinated by the end of September.

At that time, officials with the California Department of Public Health argued that the mandate was necessary as a majority of COVID-19 cases stemmed from unvaccinated people.

While unvaccinated people continue to test positive for the virus at a disproportionate rate to fully vaccinated people, health officials in recent weeks have urged that omicron’s high transmissibility makes an additional vaccine dose necessary to maintain an effective immune response.

The state has also issued vaccination requirements that K-12 teachers and state employees.

Newsom is expected to make the formal announcement Wednesday morning at a vaccination and testing clinic in Alameda County.