Newsom announced the new policy at a San Francisco Bay Area school that reopened earlier this week to in-person classes. Many California schools are back in session, with others starting in the coming weeks.

“We think this is the right thing to do and we think this is a sustainable way to keeping our schools open and to address the number one anxiety that parents like myself have for young children,” Newsom said.

Several large school districts in the state have issued similar requirements in recent days, including San Francisco, Oakland, San Jose, and the Long Beach Unified.

California, like the rest of the country, has seen a troubling surge in COVID-19 infections because of the Delta variant, which represents the vast majority of new cases. It has affected children more than previous strains of the virus.

While Hawaii Governor David Ige announced last week that all Department of Education staffers would be required to disclose their vaccination status or face weekly testing, California’s order is far more sweeping, applying to all staff who work in both public and private schools.

In the past few weeks, Newsom has mandated that all health care workers must be fully vaccinated and required that all state employees get vaccinated or choose weekly testing.

For schools, Newsom had already issued a mask mandate that applies to teachers and students but until Wednesday had left the decision of whether to require vaccines up to local districts.

As the virus has surged, particularly among children who are too young to be vaccinated, a growing number of teachers unions have been easing their opposition to vaccine mandates.

California’s two largest teachers unions—the California Teachers Association and the California Federation of Teachers—said they fully supported Newsom’s policy. Both unions cited state and national polling that indicates nearly 90% of educators have been vaccinated but said the rising spread of the Delta variant, particularly among children, makes the new policy necessary.

“Educators want to be in classrooms with their students, and the best way to make sure that happens is for everyone who is medically eligible to be vaccinated, with robust testing and multi-tiered safety measures,” CTA President E. Toby Boyd said in a statement.

Details of how the new policy will be enforced were not announced, and labor unions say those logistics still need to be worked out.

Matthew Hardy, a spokesman for the California Federation of Teachers, said the union supports the plan that allows an option for testing.

“We do not think people should lose their jobs over this,” he said.

Schools are required to be in full compliance with the new policy by Oct. 15, giving schools time to verify vaccination status and have in place weekly testing for unvaccinated staff, said Amelia Matier, a spokeswoman in the governor’s office.

Newsom did not rule out expanding the requirement to students once a vaccine is approved for children under 12 years old.

“We’ll consider all options in the future,” he said, in response to a question. “We believe this is a meaningful first step.”