Few policy proposals are so unambiguously good that no reasonable person can be in opposition. This is one of them.
Offering prizes for the successful development of vaccines for diseases that ravage the third world is a perfect idea: it taps our well-developed market system of drug research and production, providing a monetary incentive that the poor are unable to supply. Coupling the prize with a requirement to relinquish patent rights eliminates the inefficiencies inherent in monopoly drug provision, opening the market to cheap generic producers that can supply the masses.
A $10 billion prize for a malaria vaccine, for instance, would instantly spawn massive research efforts in the pharmaceutical sector. It approaches the returns from the most profitable drugs today. Even so, it would be trivial in comparison to the human benefits: 20 million lives saved within a decade, at a cost of $500 per life.
Yes, this is a liberal policy. It uses the government's resources to achieve a desirable but otherwise unachievable social end. But it is also a conservative policy. It relies entirely on markets, creates no new bureaucracy, and costs nothing unless the goal is achieved.
I don't see how anyone, except perhaps fanatical libertarians who don't think government should spend money on anything external, could possibly oppose it.