We used to do that. it was called "secondhand smoke." Eventually folks decided the side effects were bad.

It would cause people to develop widespread immune diseases as their immune system spins up ever more strongly to fight pathogenic threats.

Besides the possible technical impossibilities, there's just no reason to do so. If there are clear markings, antivaxxers would just not get inside. And people that really cannot take the vaccines due to some medical condition or young age would be exposed unnecessarily.