[xenocratus]

Poor countries might face a different issue even if they get hold of vaccines - some of them (not sure if just Pfizer's) need to be kept in really cold environments [1]. Thus some countries will struggle with distributing it.

[1] https://www.bbc.co.uk/news/technology-54889084

[bluGill]

Pfizer's is the worst, and they give you 5 days at more normal temperatures. It will be more much difficult logistically, but if needed anywhere in the world is 5 days from any place else if it is important enough.