Vaccines are a merit good. They are excludable (they can be charged for) and are rivalrous, in that different companies can produce different versions. The market could in theory therefore produce a vaccine. Start up costs are however very high, so initial average and marginal costs would be high. This is because fixed costs are high, and also because safety measures, tests, and liabilities if things go wrong, are expensive and take a long time to work through under normal safety protocols. Vaccines have high positive externalities and to really work require widespread coverage. This generally means that the social optimum for their provision will be different from the market equilibrium. This is because in a market, people will pay for the drug or vaccine up to their own marginal private cost, at the point where that meets marginal private benefit (equal to marginal social benefit.) For society, it would be better for the provision to be at the social optimum, where m...