In principle, one could get a rapid antibody test and, if negative, get a vaccine a few minutes later. For vaccines for which the vaccine has few side effects,

In principle, one could get a rapid antibody test and, if negative, get a vaccine a few minutes later. For vaccines for which the vaccine has few side effects, this is, AFAICT, not usually considered worthwhile — providers seem to prefer giving an extra MMR dose to people with unknown vaccination status for example. For COVID, at least with current vaccines, maybe it would make sense. (ISTM, based on available data, people who have had COVID ought not to be required to get two doses, but one might be reasonable from a public health perspective.)