SAN FRANCISCO (AP) — California will become the first state in the nation to require all teachers and school staff to get vaccinated or undergo weekly COVID-19 testing, Gov. Gavin Newsom announced Wednesday.

The statewide vaccine mandate for K-12 educators comes as schools return from summer break amid growing concerns of the highly contagious delta variant.

Newsom announced the new policy at a San Francisco Bay Area school that has already reopened after summer break. 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.

In the past few weeks, Newsom has mandated that all health care workers must be fully vaccinated for employment, without an option for regular testing, and required that all state employees get vaccinated or choose weekly testing.

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

On Sunday, the president of the nation’s second-largest teachers union, Randi Weingarten, said “the circumstances have changed.”

“It weighs really heavily on me that kids under 12 can’t get vaccinated,” said Weingarten, president of the American Federation of Teachers.