California Gov. Gavin Newsom on Wednesday announced a new rule requiring teachers to get a COVID-19 vaccine or be tested weekly for the virus, becoming the first state in the country to do so.

Educators must present either a physical or digital COVID-19 vaccine record card  – or a photo of a vaccine record card – starting on Thursday in order to teach in California public and private schools serving K-12 students, according to the California Department of Public Health (CDPH).

"To give parents confidence that their children are safe as schools return to full, in-person learning, we are urging all school staff to get vaccinated. Vaccinations are how we will end this pandemic," Newsom said in a Wednesday statement. "As a father, I look forward to the start of the school year and seeing all California kids back in the classroom."

Kindergarten students sit in their classroom on the first day of in-person learning at Maurice Sendak Elementary School in Los Angeles, Tuesday, April 13, 2021.  (AP Photo/Jae C. Hong)

Kindergarten students sit in their classroom on the first day of in-person learning at Maurice Sendak Elementary School in Los Angeles, Tuesday, April 13, 2021.  (AP Photo/Jae C. Hong)

More than 60% of Californians ages 12 and older are fully vaccinated, and more than 70% are partially vaccinated, though the state is currently seeing the fastest increase in COVID-19 cases with 22.7 new positive cases per 100,000 people each day, CDPH found.

More than 40% of the state's seventh- to 12th-grade students will be fully vaccinated by the start of the 2021 school year, according to CDPH.

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"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," CDPH Director and State Public Health Officer Dr. Tomás J. Aragón said in a statement. "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."

Growing numbers of pediatric hospital admissions are stirring alarm as respiratory illnesses coincide and younger children remain ineligible to receive COVID-19 vaccines amid the start of the school year.

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Hospital admissions among kids have seen an approximate fourfold increase over the last month, federal data suggests.

Children's hospitals across the country confirmed increasing numbers of pediatric inpatient volumes, including Nashville-based Monroe Carell Jr. Children’s Hospital at Vanderbilt, Children’s Hospital Colorado and Children’s Hospital Los Angeles. Texas Children's Hospital also reported an uptick in COVID-19 cases among younger residents, with the delta variant behind over 80% of new cases since July 1.

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It's not yet clear whether the delta variant is more virulent, or dangerous, among younger age groups, Dr. Richard Besser, former acting director of the Centers for Disease Control and Prevention (CDC), told "TODAY" co-hosts on Tuesday. 

"I haven't seen convincing evidence that it’s more severe," he said. "I think the jury is out on that, but just the fact that so many more children are being infected with this strain means that there will be more children who have severe disease, there will be more children who are hospitalized and, unfortunately, there will be more children who die from COVID, and that’s not something we should allow to happen."

COVID-19 vaccines are available to children as young as 12, though younger kids could become eligible for the vaccine this fall.

Fox News' Kayla Rivas contributed to this report.