Are better vaccines really better? The case of a simple stochastic epidemic SIR model

We consider a model of vaccine market where the buyer is centralized and shows an endogenous demand function based on a simple stochastic SIR model. When the seller is a monopoly, we show that better vaccines (in the sense of greater efficiency or inducing less side-effects) do not imply greater total surplus, greater buyer surplus or even greater profits. Since we consider a centralized buyer, our results cannot be caused by the well-known epidemiological externality of vaccination.