Why is it the responsibility of US taxpayers to buy vaccines for the entire world?

If people really wanted these vaccines, they would find a way to buy them themselves.

Food is more of an urgent need than vaccines, so does that mean i have an obligation to buy everyone on earth food?

I don’t support vaccinating Americans.

I don’t support vaccinating non-Americans.

And i certainly don’t support the idea of me paying to vaccinate anyone, much less everyone.