Note that when the pandemic hit, the EU room a back seat to the National governments, even though the EU has a CDC itself. And in Japan success was largely due to local effort: https://fee.org/articles/did-japan-beat-covid-19-with-a-dece...
See also: https://www.hoover.org/research/decentralize-covid-19-respon...
Without crap like that, there’s no reason California or New York couldn’t create their own medical stockpiles. They could run their own testing regime at least as effectively as the Federal government, but the FDA actually hindered testing both by the States and private companies early on due to an old regulation based in an old law that they could not shed fast enough. States were also quick to shed regulatory barriers of their own making, which should probably remain shed after this is all over.
States stockpiling or relying on Federal stockpiles or making agreements to share stockpiles is as much a choice as any other. Seeing as how the Federal stockpile was not properly maintained and refilled by either the Obama administration or the Trump administration (who could have at least checked on it) after H1N1, maybe at least one of them would manage to do a competent job of it.
I recommend listening to this podcast that outlines exactly why smaller polities were able to be nimbler: https://soundcloud.com/reuters/the-exchange-too-small-to-fai...
Yes, economies of scale provide advantages for procurement, but after a while, there are diminishing returns from more scale. That is to say, New Zealand's population is a sufficient scale, it need not pool its procurement operations with Australia. It's a key differentiator between Federalism and Individualism.