Last I checked Flu vaccines weren't mandated but recommended. Those weren't taking flu shots weren't segregated from society.
In California, kids aren't allowed in school unless they have a set of vaccines including polio, Dtap, Hep A, MMRV. . If you don't oblige, you home school your kid, this has been the rule for years.
In healthcare you can't participate unless you have MMR, TDAP, up to date ppd screenings, Hep B, and flu vaccine was mandated or you wore masks before masks were a thing.