"as many as someone will pay for" doesn't contradict "we don't have the capacity". This is a capital allocation problem and dedicating 100% of the world gdp to vaccine production will not improve our overall health and prosperity.
I'm simply saying that using more boosters in wealthy countries in no way depletes the vaccine, or raises the prices for it, in poorer countries.
I mean, would you agree that wealthy people buying more television sets does not in any way reduce the ability of poorer people to buy television sets?
But this analogy sucks because a TV is a luxury purchase and there's no network effect whereby I become safer if everyone in the world has a TV.