Unprecedented
Prior to the advent of vaccines, there was no synagogue in the world that had a policy, "Unless you've already had [fill in communicable disease] you are unwelcome here." Nowadays, someone who gets measles is a pariah, even though after the fact, the person has the best immunity for measles. Natural immunity. Those who have not had measles - either they have immunity or they do not (many adults have waned immunity if they haven't received boosters, and even vaccines and boosters are not 100% guaranteed). So now we are establishing a new rule! Being part of the Jewish community is contingent on being fully compliant with the CDC recommended schedule. Of course this rule only applies to children! Adults who are not up to date are welcome. We think. We're not sure. We don't want to tell adults what to do - even though we are happy to treat them like children, and assume things about their intelligence.