I wouldn't define United's system by its ability to do any of those things reliably, but to each their own

I don't think this will be helpful. I barely want some FA's serving me a drink much less a vaccine.

The best course of action is a national immunization plan that leverages the full extent of the health care system -- doctors, dentists, ophthamologists, veterinarians, etc. Hospitals, urgent care clinics and ER's are very busy -- but some of the specialty doctors are not, and these people are all readily trainable to deliver vaccines.