Paying For Developing World Vaccines

How do you reconcile a humanitarian need (vaccines for diseases that effect millions in the developing world) with the necessary exigincies of the free market (people in the developing world can’t afford to pay enough for the vaccines to justify the research necessary to develop them) without substituting heavy-handed and ineffective government coercion for market efficiencies? One option is to fund advance market commitments, in which a developed world government promises to buy a certain (substantial) quantity of vaccines if and when they’re developed.