The California State University System said Tuesday it will require faculty, staff and students who come to campus in the next school year to be immunized against the coronavirus even if federal regulators have not yet given full approval to a vaccine.

Cal State is the nation’s largest four-year public university system, with about 485,000 students on 23 campuses. Its announcement reflected worries among many education leaders, at schools such as the College of William & Mary and the State University of New York, about the threat the virus’s delta variant poses to the reopening of school.

In April, Cal State leaders had said they planned to implement a vaccine mandate after the Food and Drug Administration gives full approval to at least one of the shots that now have emergency-use authorization. But Cal State now is removing that caveat and accelerating the mandate. Its decision follows a similar recent action by the University of California system.

"The current surge in COVID cases due to the spread of the highly infectious Delta variant is an alarming new factor that we must consider as we look to maintain the health and well-being of students, employees and visitors to our campuses this fall,” Cal State Chancellor Joseph I. Castro said in a written statement.

In a telephone interview, Castro said all 23 campus presidents agreed Friday to move forward with the requirement. Vaccinating as many people as possible, he said, is “the safest, most effective way to reopen our campuses to a majority of in-person courses.”

Cal State said faculty, staff and students must certify their vaccination no later than Sept. 30. The deadlines could be earlier on various campuses. There will be exemptions for religious and medical reasons and for people in the university community who do not come to campus. System officials said they would confer with labor groups about how details of the mandate affect employees.

Hundreds of colleges and universities are requiring coronavirus vaccination as they prepare to start the school year. But many others are strongly encouraging vaccine doses, without a formal requirement.

The issue has become a flash point in recent weeks. Last week a federal judge upheld a vaccine mandate at Indiana University after some students alleged in a lawsuit that the policy violated their bodily autonomy and medical privacy. The judge found the university could proceed even though the most widely circulated vaccines, from Pfizer-BioNTech, Moderna and Johnson & Johnson, are being distributed under emergency-use authorization.

Weighing their policies, many schools and employers are hoping the FDA will act soon on vaccine approval applications. Full approval of one or more vaccines is possible in coming months. Some federal officials are hopeful that could happen by the end of summer, to help promote vaccination in response to a pandemic that has killed more than 611,000 people in the United States.

Some students are pushing back against mandates. One group called Young Americans for Liberty is circulating a petition opposing “forced vaccinations at Virginia Tech.” Ben Walls, a junior from Richmond, who is a leader in the group, said he appreciates that the public university offers a religious exemption from its vaccine mandate. But Walls said he worries nonetheless that the school might impose additional restrictions and viral testing protocols on the unvaccinated. “We’re going to be treated more or less like lab rats,” he said.

With or without mandates, universities are anxious to maximize vaccination. The State University of New York, another major public system, plans to enforce an immunization mandate at its campuses, contingent on full FDA approval of a vaccine. SUNY Chancellor Jim Malatras said he believes about 60 percent or more of students have received at least one shot so far. The share will climb, he said, as officials point out that unvaccinated students will be required to undergo viral testing, wear masks and follow other public health restrictions. “The ultimate goal is to get everyone vaccinated,” he said.

Some William & Mary parents were startled to learn Monday in an email from administrators that vaccination rates were well below what had been expected and what will be needed for a more normal school year.

The public university in Virginia had announced in May that vaccination would be required for students and employees once the FDA gives full approval to at least one vaccine. Now William & Mary officials are considering speeding up the requirement.

As of mid-July, 56 percent of students had registered as fully vaccinated, according to the email from vice president for student affairs Ginger Ambler and chief operating officer Amy Sebring.

“Right now, our reported numbers fall well below a level that would allow William & Mary responsibly to continue planning as we were,” they wrote. Without significant improvements, they wrote, the university could be forced to impose limits on social gatherings, sporting events and other activities, and reinstate broad mask requirements.

Response from parents was immediate and heated. One mother wrote in an online group that the school should not push an experimental drug on students. Another said anyone hesitant to get a vaccine could attend school virtually, rather than put others at risk. Many vowed to plead with school leaders for a mandate.

“I was in complete shock,” Amy Zamboldi, a parent from New Jersey, said of William & Mary’s Monday warning. Zamboldi said it would be crushing for her son, a rising senior, to miss out on another normal year of college. She would worry about his and others’ health if vaccines were not mandated. And classes start in just weeks. “Time is ticking,” she said.

By Tuesday morning, William & Mary spokesman Brian Whitson wrote in an email, the share of students verified as fully vaccinated had jumped to 64 percent.