STORRS, Conn. — There’s been a mix of coronavirus requirements at universities and colleges in the U.S.

At most of the largest public universities, students aren’t obligated to be vaccinated against COVID-19. Some schools do require vaccines, but with leniency for those who opt out. Still others have expelled students who don’t comply.

An analysis by The Associated Press shows 26 of the nation’s 50 largest public universities aren’t requiring the vaccination.

Universities with vaccine mandates are concentrated in the Northeast and California. Most without mandates are in states that restricted the ability to implement vaccine requirements, including Florida, Texas and Arizona.

As a new semester begins amid a resurgence of the coronavirus, administrators and faculty nationwide see high vaccination rates as key to bringing some normalcy back to campus. Where mandates face political opposition, schools are relying on incentives and outreach to get more students vaccinated.