Equilibrium vaccination patterns in incomplete and heterogeneous networks

Under-vaccination is a usual concern of disease control studies, but this paper employs a simultaneous-move game in a three-agent contagion network to show that it is only one of the three inefficient patterns. When the network structure is incomplete or individual characteristics are heterogeneous, there exist new types of Nash equilibrium outcomes with either the right number but wrong set of people getting vaccinated or too many vaccinations, and these equilibria are robust to standard refinements. While untargeted policies can correct the standard under-vaccination problem, targeted policies are more palatable for correcting the new inefficiencies. Universal mandates can never improve on any Nash equilibria.