Vaccinated or not, here they come.

College students are flocking to campuses across the country for a school year they hope will mark a full return to the academic and social life so often denied them for the past year and a half of the coronavirus pandemic.

Yet the delta variant’s summer surge, driving viral infections and covid-19 hospitalizations higher from coast to coast, now looms as a dangerous threat over what many had thought would be a celebratory moment for higher education. It raises the stakes in the divide between schools that mandate vaccination against the virus and those that do not. And it has inflamed debate over whether and how long students and professors must wear masks indoors.

Divya Shah, 18, of Rochester, N.Y., masked up as she moved into her dormitory one recent day at Georgetown University in D.C. She had complied with the university’s order to vaccinate, and she was eager to jump into the freshman experience after being forced to miss homecoming and other rituals during a high school senior year almost entirely online.

“It feels really exciting. The students last year didn’t have this opportunity,” Shah said. “I’m looking forward to being in person with everyone.” But she knows, too, that outbreaks could disrupt or derail the university’s plans. “I’m really hoping we don’t get sent home,” Shah said.

Among faculty there is delight and, in some places, dread at the resumption of face-to-face instruction. Professors, too, are craving live contact with students after a string of exhausting semesters of remote and hybrid teaching. But they worry about what will happen in packed lecture halls and seminar rooms if unmasked students are carrying a virus that has killed more than 631,000 in the United States.

“We’re terrified and we’re angry,” said Leslie A. Schwalm, a professor of history and gender, women’s and sexuality studies at the University of Iowa. The state’s public flagship university requires neither vaccination against the virus nor indoor mask-wearing. Schwalm, 65, who has been vaccinated, said she will be teaching in a small classroom with 35 students and practically every seat filled. She fears catching the virus and transmitting it to her elderly father or others who are medically vulnerable.

It is “immoral,” Schwalm said, for the university not to require masks indoors. “No one I know wants to teach virtually this year. We want to be in the classroom. We want to be safe in the classroom. It’s eminently clear how to do that.”

University of Iowa President Barbara J. Wilson, who took office in July, is navigating the crosscurrents of a Big Ten university and a Republican-led state government generally hostile to vaccine and mask mandates. About 55.7 percent of Iowans had received at least one vaccine dose as of Wednesday, according to a Washington Post analysis, below the national average of 60.9 percent.

“President Wilson understands the concerns of some of our campus community and has been in constant communication with the presidents of our sister institutions and Board of Regents leadership to share those concerns,” the university said in a statement. “She is doing everything she can to strongly encourage students, faculty, staff, and visitors to get vaccinated and wear masks on campus.”

So far, the second fall term of the pandemic is opening on college campuses more smoothly than the first. “It’s back to life,” said Preeti Malani, the University of Michigan’s chief health officer and a professor of medicine in infectious diseases. “We’ve been waiting 18 months for this. I am optimistic.”

The university requires vaccination. However, hundreds of Michigan faculty members are seeking more flexibility to teach remotely and other protections. A petition they signed cites “growing evidence that one cannot rely on vaccination alone to mitigate the spread of COVID-19”

A year ago there was chaos in various places as viral outbreaks forced major universities to empty classrooms and, in some cases, residence halls on short notice. Many students stayed home for much or all of the year. Schools struggled to find the right ways to teach under unprecedented public health restrictions: face-to-face, online or some combination. They also faced enormous expense and logistical challenges in testing students and employees for the virus.

The emergence of coronavirus vaccines and lessons learned from the last school year have given colleges more confidence. Full federal approval this week of the Pfizer-BioNTech vaccine, a milestone that could spur more inoculations nationwide, provided another boost.

“This year is different because we have a vaccine and a multilayered strategy — testing, vaccinations, mask mandates — to keep our community safe,” said Paula A. Johnson, president of Wellesley College in Massachusetts. “As time goes on, we are going to need to learn how to live with this virus. And I think we’re learning that right now.”

“There is always anxiety, but we feel like we’re on much firmer ground,” James Malatras, chancellor of the State University of New York, said in a text message. The SUNY system, one of the nation’s largest, will require students to get vaccinated.

In all, the Chronicle of Higher Education counts more than 700 colleges and universities with vaccine mandates. Typically they offer medical and religious exemptions. Federal data from fall 2019 analyzed by The Post shows these schools account for an estimated enrollment of 6 million students.

But far more students — more than 12 million as of Wednesday — are projected to attend colleges that do not require coronavirus vaccination. Many schools without vaccine mandates are located in Republican-led states, reflecting political divisions on vaccine policies. About half of state flagship universities do not have vaccine mandates. Nor do most historically Black colleges and universities.

The situation is fluid. Louisiana State University, in a state with spiking infection rates, announced a vaccine mandate Tuesday. So did Ohio State University, which will require students, faculty and staff to get their first shot by Oct. 15. Other schools are seeking to maximize vaccination through incentives and encouragement.

Florida A&M University, in a state that does not allow vaccine mandates at public universities, reported as of Monday that 74 percent of students in its residence halls were fully or partially vaccinated. It has dangled $100 cash awards, laptops and iPads as prizes to push students to get shots. “It’s been an all-out press,” said Larry Robinson, president of the historically Black university in Tallahassee.

Experts say many students nationwide are on board with the goal.

“Students are getting the vaccine because they want to live out their dream,” said Chris Marsicano, an assistant professor of educational studies and public policy at Davidson College in North Carolina, who has tracked vaccine policies. “They are not messing around with this. They don’t want to be in their parents’ basement playing Xbox.”

In the Washington region, most colleges are requiring vaccination. American University President Sylvia M. Burwell cited that policy as a key step in bringing students back to the D.C. campus. Ninety-five percent of students are fully vaccinated, Burwell said Monday, and she expects the share to grow as international students and others complete their doses. Ninety-eight percent of full-time faculty and staff members are vaccinated.

With high vaccination rates, AU is not “in a place where we’re going to do shutdowns, lockdowns, that kind of thing” — as long as officials can continue to screen for the virus and the vaccines remain effective, Burwell said.

On Monday, Emma Miloglav, 19, waited in line at AU’s student center for an identification card. She is among many college students nationwide whose freshman year was utterly upended by the pandemic. Now a sophomore, Miloglav had never even had a student ID or been on campus until this week. She can finally walk the quadrangle, live in a dorm, go to class with a backpack, study in a library.

“It’s refreshing, but it’s also really weird,” Miloglav said. She spent her freshman year online, taking classes from her hometown of Sebastopol, Calif. While Miloglav is happy to be in Washington, she expects the pandemic to continue to affect college life. “It still doesn’t feel normal,” she said. “Everything is modified.”

Disruptions have emerged elsewhere. Rice University, which requires vaccination, moved most classes online for the first two weeks after viral testing on campus showed unexpectedly high infection counts. Some of the results turned out to be false positives, but the university said it remains cautious because of a viral surge in its home city of Houston.

California State University at Stanislaus, known as Stanislaus State, pushed its classes online until Oct. 1 after the virus swamped surrounding Stanislaus County and started making inroads on the Central Valley campus.

“We’d never seen a spike in cases like that before,” said Ellen Junn, the university president. “There were 740 new cases in the county in one day. I felt we had to protect our students, faculty and staff.” The delay, Junn said, will buy time for the university community to comply with its vaccine mandate. Progress has been slow in a county where fewer than half of eligible residents are fully vaccinated.

“We’re disappointed it came to this,” said David H. Colnic, a political science professor and head of the faculty union at Stanislaus State, “but there is a considerable amount of relief.”

But Noelle Heckinger, 21, a senior in English, felt let down. Vaccinated months ago, she said her nerves were frayed by the isolation of learning online for three straight semesters. After transferring to Stanislaus State during the pandemic, she was eager to meet classmates on campus for the first time.

When she learned of the delay, “my heart sunk,” Heckinger said. “I realize the university has a heavy burden of trying to protect people … but why couldn’t they implement the vaccine requirement sooner? I think most of us are willing to do whatever it takes to get back to campus.”

Some faculty in schools without vaccine or mask mandates are drawing a line.

Cornelia Lambert had been looking forward to teaching this fall at the University of North Georgia, especially a class on the history of infectious disease that explores the medieval plague and other catastrophes. The 45-year-old academic and her husband have health concerns that make them vulnerable to the coronavirus. Last school year, she taught online. This school year, Lambert said, she was told she must teach in person.

After many nights of staring at the ceiling, trying to decide what to do, Lambert said, she resigned from her position as a lecturer. She said she did it to protect her husband — and on principle. “I feel like it was socially irresponsible for all these universities to tell kids, ‘We’re back to normal. Come on down!’”

Some will dismiss the risk. But people often don’t know about the health conditions of others, Lambert said. “I know my colleagues think I’m wackadoo,” she said. “But I don’t care.”

A university spokeswoman did not respond to a request for comment. The school’s website encourages people to get vaccinated and wear masks indoors.

Clemson University’s president, James P. Clements, raised a stir on Aug. 13 when he posted a picture on Twitter that showed an indoor arena full of new students seated close together and mostly unmasked at a convocation. “Welcome to the #ClemsonFamily,” he wrote. (The president himself did wear a mask.)

Critics said Clements had sent a poor public health message at a precarious moment as the delta variant was rampaging through South Carolina. “When I first saw the picture, I figured some student had taken it and posted it,” said Jordan Frith, an English professor. When he realized it came from the president’s social media account, “that made it, in my opinion, far more ominous.”

Rebekah Noell, the stepmother of a Clemson student, said the university must show more caution. “You can say you’re encouraging masks, but when you’re the president and tweeting out pictures” of unmasked students, she said, “it sort of strikes fear into the heart of a parent that you’re not really setting an example.”

Asked about the incident, Clemson spokesman Joe Galbraith noted that the public university held another convocation on Aug. 16, this one for transfer students. Masks were placed on each seat before they arrived. The Greenville News published photos showing nearly all students wearing them.

On Aug. 17, the South Carolina Supreme Court issued a ruling that allowed public universities to institute an indoor mask mandate, which Clemson promptly did for the first three weeks of the term. The university does not mandate vaccination, but it does require all students to be tested once a week for the virus regardless of vaccination status. Through Monday, the share of tests showing positive coronavirus cases was below 1 percent — an encouraging sign, officials said.

“The University continues to evaluate all public health data as it mitigates the prevalence of COVID-19 while maximizing opportunities to continue in-person classes,” Galbraith wrote in an email.

Some students have protested the mask requirement as a needless burden, according to local news reports, but many appear relieved that Clemson is opening so far without disruption and that cherished rituals, like the Tigerama homecoming pep rally, are back. Sophie Finnell, 21, a senior in psychology from Greenville, S.C., said she is vaccinated and unbothered by the need to wear a mask. What matters most to her is the change in atmosphere: “Energy and buzz,” she said.

Last year, she said, it felt lonely and isolating and tedious to take classes mostly online. “This year, there’s no other way of saying it, campus feels alive again,” Finnell said.