I wouldn't want to be first in line anyway but I wonder how common it is for allergies to make a vaccine not safe for use?

This does not surprise me. I have a friend whose son had severe food allergies as a child and teen. He could not eat anything with dairy, and is still wildly allergic to nuts and shellfish. I remember the first Thanksgiving they had after he finally received a diagnosis was a challenge for her. She had to not only exclude everything from eggs to dairy to I think even certain grains, she had to buy expensive food to assure there was no cross contamination.

The biggest worry was keeping up his vaccinations, because egg is used as some sort of component with some vaccines. I don't know the exact details. I just remember her getting upset because some asshole political cartoonist made a comic where he basically said parents saying they don't want their kids vaccinated are the same parents who want special treatment if their kid has a food allergy.

I remember telling off the cartoonist on Twatter at the time. Didn't do any good except made me feel just slightly better.

But anyway, yeah, this doesn't surprise me. With any luck they will be able to develope the vaccine without having to mix it with any known food allergy culprits

Oh no... the antivaxxers are going to flood this place.