[IfOnlyYouKnew]

The US just signed two contracts for additional deliveries of 100 million doses each of two vaccines (Pfizer & Moderna, I believe?)

I doubt that these companies can make such deliveries without first fulfilling the contracts they have with the EU. I looked it up at the time, and they have. contracts with hundreds of millions of doses for the EU.

So what I believe will happen is that deliveries will grow extremely fast at some point before July, when new production capacities come online.

Consider what would happen if capacities increased dramatically: any advantage some countries have right now will shrink, when measured in time, from "months" to maybe just a few weeks. The real end of lockdowns may well still coincide.