I think the US should follow the UK in prioritizing the 1st vaccination to as many people as possible instead of saving enough doses for the same people to get the 2nd one. The UK is stretching the gap between doses from 21 days to 12 weeks. I realize there isn't a ton of data on efficacy after only 1 vaccination, but I believe it won't be far off what you get with 2 vaccinations and you can protect more people now.
I think getting ~75% efficacy to twice as many people is better than ~95% to half as many. I think the anamnestic response will still be quite strong at 12 weeks.
It's been a while since I saw the literature
But I believe one of the major vaccine companies published something along the line of 53% immunity 10 days after the first shot
Fairly certain it wasn't close to 75%
I think the bigger concern is how long will it last after only one shot, and I certainly don't remember reading that