Some people might be allergic to things that may be in the vaccine and are completely unable to get the vaccine

Yes. But, this is for a state licensed doctor to determine and not something somebody just wakes up one day and decides they have a condition...

or is told that they have a condition from an unlicensed unaccredited holistic healthcare provider.

Doctors already do consider valid allergic reactions to the vaccines and recommend people dont take them in those instances. Such as phenols or eggs.

Very common in a lot of people who take insulin as well. But, their are ways around it.