CtLawyer, am I reading you correctly – you got first vaccine and went to shul the next day?
Even lawyers get emotional? You are not having any immunity until next shabbos.
Not a scientific observation, but a common sense one, that might later be confirmed by an experiment: those, especially elderly, who had no side effects should be more careful as possibly their immune system is not responding well. Especially w/ Moderna, as they seem to have used a higher dose in Phase 3 to make sure they pass the criteria. A later antigen test would be another data point, although researchers warn of low reliability. Again, these ideas are not (yet, unfortunately) tested.