Early in the pandemic it seemed plausible that it was hard to scale up production, and that it was tough to quantify the marginal cost as a $/dose. But given how long it’s been that no longer seems plausible.
I’ve heard low numbers like $10/dose, but I’ve never seen a useful discussion or citation and it’s not easy to track down on google.
My assumption is that even if the number is higher than that, it’s still low enough that this is essentially negligible when deciding on booster shots in the developed world. (And that we could probably decrease the size of doses to drive down costs further.)
Supply constraints remain significant and the lack of mRNA vaccines in China is one potential piece of evidence to support that.
I think the story has to be something like "given the prices they will be allowed to charge, no one is building new manufacturing capacity. So after the capacity for operations warp speed (~200M doses over 6 months?) was built, they have just been running those factories at full speed and this is still vastly less than world wide demand.
But asking about "marginal price" is still maybe not that meaningful, the price will depend on when you want to get the goods.
I guess this is what "constraints" really amount to, but I remain skeptical that either we couldn't put a price on it if we knew what was happening, or that the price would be more than $100/dose.
Perhaps something along the line cutting down the dosage and then that would drop the price of the hard-to-scale manufacturing linearly.