I’m not exactly sure what you mean by a 100% covid vaccine population… Most schools I am familiar with are mandating vaccines but do allow waivers for religious and medical reasons. Based on posts on a parent FB group, several students at the school my D will attend filed the waivers. I would be surprised if that option goes away. I’m not sure if that is acceptable to your family.
As others said, there is not much to do other than research the policies followed this year to get a sense of a college administration’s approach.