And I was busy this weekend.
Noting my boundless ignorance, we seem to have made decent progress on vaccines for similar viruses before (although they quickly proved to be of little value because containment was much easier in those cases) and coronaviruses apparently generally lend themselves to vaccines in some important respects (limited mutation speed). (But I was taking TBC's claim as given.)
But how useful the acquired immune response is, and how long it lasts, does still seem to be a bit up in the air - hence "half-way effective" and vaguely wondering about problems of actually using the vaccine to slow spread, let alone eliminate COVID-19.