INDIANAPOLIS (AP) — The quickly approaching fall semester has America’s colleges under pressure to decide how far they should go to guard their campuses against COVID-19 while navigating legal and political questions and rising infection rates.

Hundreds of colleges nationwide have told students in recent months they must be fully vaccinated against COVID-19 before classes begin.

California State University, the country's largest four-year public university system, joined the list last week, along with Michigan State University and the University of Michigan. Their announcements cited concerns about the highly contagious delta variant and came as the Centers for Disease Control and Prevention issued updated mask guidelines based on new research regarding its spread.

CSU Chancellor Joseph I. Castro called case surges linked to the variant an “alarming new factor that we must consider as we look to maintain the health and well-being of students, employees and visitors.”

Yet many more colleges have held off on vaccine mandates in a reflection of the limits school leaders face in adopting safety requirements for in-person classes.

In many Republican-led states, governments have banned vaccine mandates, or school leaders face political pressure to limit their anti-virus actions even among students who live in packed residence halls. Opponents say the requirements tread on personal freedoms.

Some campuses have sidestepped pushback by instead offering enticements, such as prize drawings for free tuition and computers, as they seek to boost student vaccination rates to 80% or higher.

And a few have gone against the grain of their GOP-led states, such as Nova Southeastern in Florida requiring employees to get the shots and Nebraska Wesleyan mandating vaccinations for its 2,000 students.

Private colleges like these have more legal leeway regarding coronavirus rules, experts say. Prominent private universities mandating student vaccinations include Harvard, Yale, Notre Dame, Northwestern, Duke and Stanford.

University of California law professor Dorit Rubinstein Reiss, who writes and teaches about vaccine law, said the biggest legal gray area is whether colleges can require the COVID-19 vaccines while they remain under federal emergency use status.

Courts will likely allow university leaders to take such steps to protect student health, but many colleges can’t avoid the reality of states taking a stance against vaccine mandates, Reiss said.

“Especially a state university, going against the prevailing political view is probably going to be short-lived,” Reiss said.

Coronavirus politics have been a complicating factor for the vast majority of campuses without vaccine requirements, said Dr. Michael Huey, interim CEO of the American College Health Association, which in April recommended vaccination mandates for all students taking on-campus classes.

“If you set up a situation where you can’t require vaccination, you can’t ask about vaccine status and you can’t have required testing or mitigation strategies, like masking, it can’t be safe,” said Huey, former executive director of student health services at Emory University in Atlanta.

Indiana University has so far prevailed against a court challenge to its student vaccine requirement, which school officials say is a “clear path forward” to removing limits on in-person classes, sporting events and social activities.

Noah Hamilton, who’ll be a sophomore at Indiana’s main campus in Bloomington this fall, said he had anxiety about getting the shots and likely wouldn’t have done so without the requirement.

“But I don’t want to be stuck doing 100 percent online," Hamilton said. "I want to be back on campus and actually trying to have a normal college experience.”

Among the some 4,000 college campuses across the country, more than 600 have imposed a vaccine mandate, according to tracking by the Chronicle of Higher Education. But their requirements vary.

The University of Washington and the University of Maryland, for example, are among the public schools mandating shots for both students and employees. The University of Connecticut and the University of Maryland require the doses for students but not faculty or staff.

In some cases, union contracts or state laws prevent schools from requiring staff member vaccinations.

Meanwhile, the University of California and California State University — California’s two major state systems, with more than 750,000 total students — initially were holding off on inoculation requirements until at least one COVID-19 vaccine had full Food and Drug Administration approval. But both have now mandated shots for students and employees.

Religious and medical exemptions from vaccine requirements are commonly offered, although the universities are generally making those students undergo frequent COVID-19 testing and wear masks in public areas.

Opponents of student vaccine requirements have gone to federal court challenging mandates issued by Indiana University, the University of Connecticut and the California State system.

In the first ruling among those cases, a judge last month rejected arguments from eight students that Indiana University’s requirement violated their constitutional rights to “bodily autonomy” by forcing them to receive unwanted medical treatment.

A court in Chicago also denied an appeal from their attorney, James Bopp, who’s been prominent in many conservative political causes. Bopp works with the group America’s Frontline Doctors, which criticizes the COVID-19 vaccine and has been widely discredited for spreading disinformation about the coronavirus and unproven treatments.

Bopp said hundreds of people across the country have contacted him wanting to challenge vaccine mandates. He argues the students he represents, primarily young adults, are at low risk of severe COVID-19 illnesses while facing possible dangers from the vaccine being administered under federal emergency use authorization.

“Why are they being targeted for a vaccine that older people aren’t required to take even though their risk is enormously greater?” he said.

Indiana University says nearly 85% of its students have reported receiving at least one dose. Purdue University, Indiana’s other Big Ten school, isn’t requiring vaccinations but is telling students who don’t submit documentation that they could face weekly COVID-19 tests.

Purdue, which says at least 60% of students are vaccinated, tried to entice students to get the shots with 10 prize drawings for a full year’s tuition.

Many other schools are offering similar incentives, such as the University of Wisconsin’s regional campuses giving away 70 $7,000 scholarships to vaccinated students at sites with at least 70% vaccination rates. Missouri State has a $150,000 program with prizes that include free tuition, meal plans and computers.

Face masks won't fade away as much as hoped on campuses this fall, either. Purdue and the University of South Carolina were among those in the past week to announce a return to required masks following the new CDC guidance that fully vaccinated people wear them indoors if they live in areas with high virus transmission rates.

Rachel “Rae” Applegate, an incoming Notre Dame freshman, was vaccinated this summer with her 16-year-old sister and said she was hesitant because the vaccines are so new. She also feared a greater risk of COVID-19 exposure on campus than at home in Evansville, Indiana.

“I can understand people’s concerns about not wanting to be told what to do, but to me, this (getting vaccinated) just makes sense,” Applegate said. “When we’re all together on a campus like this … and with the variants and everything else, it’s like, don’t we all want to be as safe as possible?”

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Associated Press writer Casey Smith contributed to this report.