This, of course, is the biggest concern. Luckily for the US rural population, residents either work really spread out (ranching, ma & pa garages, small community stores), where social distancing comes naturally, our commute to somewhere like a May packing plant or factory where large scale distribution could probably be coordinated with clinics in the area. These folks often need to come to population centers where a little planning can get them an appointment pretty easily if they want a vaccine.
For the underserved nations, if something isn’t figured out for longer term stability, I naturally agree the world population has a way to go to be out of this.