LOS ANGELES - California Governor Gavin Newsom announced Wednesday the most populous state in the United States will implement first-in-the-nation measure to require all teachers and school staff to get vaccinated as schools return from summer break amid COVID-19 delta variant spread.

Newsom noted in a news conference at a Northern California school that "this is the right thing to do."

"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," said the governor, adding that "schools are doing everything in their power to keep our kids safe, to keep our kids healthy."

Newsom said an impressive $124 billion is being invested in California's public education system this year to implement various school initiatives, including supports for physical and mental health as well as the social-emotional and academic needs of students.

According to the new public health order issued by the California Department of Public Health, all school staff are required to either show proof of full vaccination or be tested at least once per week. The new policy will take effect Thursday and schools must be in full compliance by Oct 15.

"There's no substitute for in-person instruction, and California will continue to lead the nation in keeping students and staff safe while ensuring fully open classrooms," said Tomas J. Aragon, director of the California Department of Public Health and the State Public Health Office in a news release.

"Today's order will help the state's continued efforts to increase vaccinations, similar to the orders encouraging state and health care workers and businesses to get vaccinated," he added.

The state's two major teachers unions - the California Teachers Association and the California Federation of Teachers - applauded Newsom's decision.

"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," said California Teachers Association President E. Toby Boyd, adding that Newsom's announcement is "an appropriate next step to ensure the safety of our school communities and to protect our youngest learners under 12 who are not yet vaccine eligible from this highly contagious Delta variant."

California Federation of Teachers President Jeff Freitas also noted the policy with mitigation measures like masking, hand washing, and good ventilation "will ensure we are doing everything possible to keep schools safe for in-person learning."

California State Parent Teacher Association (PTA) President Carol Green echoed their opinions, "We want to do everything possible to protect our most vulnerable children and ensure that all children can return to school as safely as possible."

"We stand by our position that educators are essential workers and support the safe opening of schools to in person instruction," Green said.

There are around 6 million children and young adults in more than 10,000 schools with 300,000 teachers in the state's public school system, according to the California Department of Education.

State data showed that 63 percent of Californians 12 years of age and older are fully vaccinated with an additional 10 percent partially vaccinated.

Less than 41 percent of Californians 12 to 17 years old were fully vaccinated as of Tuesday. Children under the age of 12 are not currently eligible for any authorized vaccines, according to the California Department of Public Health.

The department noted in a Wednesday's release that California is currently experiencing the fastest increase in COVID-19 cases during the entire pandemic with 22.7 new cases per 100,000 people per day, with case rates increasing ten-fold since early June. Officials said that the Delta variant, which is two times more contagious than the original virus, is currently the most common variant causing new infections in California.

Although vaccination mandate against COVID-19 is generating controversy and the pushback in some US states, California officials insist vaccination is the most effective means of preventing infection with the COVID-19 virus.

Once the epicenter of the pandemic in the country, California reopened its economy in June. The state saw a rapid rise in new cases and hospitalizations in summer, but it's still lower than the national average. California, home to around 40 million residents, has 3,969,722 confirmed cases of COVID-19, resulting in 63,976 deaths, to date.