> I don't think we have ever been forced between these two scenarios
I'm not sure; January->April the US was constrained by vaccine supply. The initial rollout to at-risk groups was not a case of "we got a shipment of 100m doses, now we need to figure out how to use them", it was more "we're manufacturing 1-2m doses per day and trying to ramp that up". It took months to go through the gradually broadening risk tiers. (e.g. see https://investors.modernatx.com/news-releases/news-release-d..., which says "deliver 100m vaccines by end of March, 100m more by end of May").
I believe the US was keeping shots back in favor of using them later as second doses, rather than giving them immediately as first doses, though I don't have a citation for that to hand. If that's right, the US could have ~doubled its rate of vaccination, i.e. got to the April 15 "all age group open vaccination" milestone in 2 months instead of 4 months, with first doses only administered to that population. At the very least, we were giving second doses in Feb (21-28 days after first doses in Jan) that could have been given as first doses to the higher-risk groups we were still prioritizing through April.
There's a follow-up question on which I have not run the numbers -- are there any X,Y pairs for which you'd rather hold back a shot to give as a second dose later for a >X year old, instead of giving it immediately as a first dose to a <Y year old. Interesting question, I don't think that's what you were getting at though.
I'm not sure; January->April the US was constrained by vaccine supply. The initial rollout to at-risk groups was not a case of "we got a shipment of 100m doses, now we need to figure out how to use them", it was more "we're manufacturing 1-2m doses per day and trying to ramp that up". It took months to go through the gradually broadening risk tiers. (e.g. see https://investors.modernatx.com/news-releases/news-release-d..., which says "deliver 100m vaccines by end of March, 100m more by end of May").
I believe the US was keeping shots back in favor of using them later as second doses, rather than giving them immediately as first doses, though I don't have a citation for that to hand. If that's right, the US could have ~doubled its rate of vaccination, i.e. got to the April 15 "all age group open vaccination" milestone in 2 months instead of 4 months, with first doses only administered to that population. At the very least, we were giving second doses in Feb (21-28 days after first doses in Jan) that could have been given as first doses to the higher-risk groups we were still prioritizing through April.
There's a follow-up question on which I have not run the numbers -- are there any X,Y pairs for which you'd rather hold back a shot to give as a second dose later for a >X year old, instead of giving it immediately as a first dose to a <Y year old. Interesting question, I don't think that's what you were getting at though.