For me, it's one thing in a long list. I don't ask at interviews, and as I rarely work infants (never under 6 months), I've never been asked.
On a separate note, I have a poa for my current charges. I requested the exemption forms, signed and had them notarized, filed them with school and doctor, all per my DB's instructions while he was out - of - state. Oh, and scheduled medical/dental, took kids, enrolled and withdrew, etc.
Vaccine or no vaccine is one small thing in a very long list of pros and cons about family.