The H.I.V. advocacy group PrEP4All estimates that for $4 billion — less than the country is spending per day on coronavirus response efforts — the federal government could build enough manufacturing capacity to vaccinate the entire planet against the coronavirus. It will cost much more to actually make the needed doses, of course. The nonprofit advocacy group Public Citizen estimates that a $25 billion governmentwide initiative would produce around eight billion doses of mRNA vaccine, or enough to vaccinate half the planet. That’s far less than the trillions that could be lost if the economy contracts further as the pandemic persists.