If you think of state governments as basically being as permissive as possible consistent with not overwhelming their hospital systems then even vaccinating 20% of the population has a huge economic impact as long as it’s targeted in a halfway plausible way.
That is from Matt Yglesias. I would stress also the bad news that in the meantime many Americans (other citizens too!) are becoming infected. I haven’t seen recent serological results, but quite some time ago the range already was 10-15% of America infected. It seems entirely plausible to think that many parts of the country (not SF, not Vermont) will be at 30% or higher infected by February. Plus 20% getting vaccinated, and still likely a residue of the population with above average protective immune response, and by that I mean relative to age group.
So overalI I am more optimistic about the spring than are many of the people I am talking to. And the United States may well be the first country to arrive at a semblance of herd immunity, albeit not the way we might have preferred.