My fantasy vaccine technology would be microencapsulation. There is no reason why all vaccines couldn’t be given by mouth. This would address the most common concern parents have: painful injections. Microcapsules could be constructed to survive the acid-protease environment of the mouth and stomach and be made in such a way that antigen release could occur in the small intestine, which is a rich source of B cells, T cells, and antigen presenting cells. Also, microcapsules could be targeted to specific antigen-presenting cells depending on the type of immune response desired.
The problem is that this would be a lot of work and there is very little financial incentive to do it. But as long as we’re dreaming, this is mine