Instead of deciding in advance which vaccine candidates deserve funding, however, a government could commit itself to paying a reasonable price for whatever vaccine turns out to work, effectively guaranteeing a market for it. Drug companies would thus have an incentive to invest in promising candidates. Rather than pushing vaccines into existence, this approach pulls them.
However, this merely makes complex what is in actuality a fairly simple truism. When the government forces down the price of something in order to make it "cheaper", a shortage is likely (if not inevitable). Instead, if a reasonable price is obtained, the product becomes more available.
Government intervention, I would argue, cannot remedy scarcity (except briefly), but it can intensify it.