The Question
Considering both epidemiological and economic concerns, what is the optimum level of control of immunizing infections? How does this vary on a local and global scale for weakly and strongly coupled populations?
What We Found
The economic optimum is to tolerate some cases of less serious infections, especially if vaccination costs are high.
Why It Matters
The results show that the strength of coupling between populations has important consequences for incentives of local decision makers. Focusing on local budgetary limitations, we find the present value of infecteds is so high in short-term cost-effective strategies that the cost of current infections outweighs the benefit of preventing cases in the future. Long-term optimal strategies, on
the other hand, stress the value of herd immunity to the extent that it might make sense for a patch to spend on vaccination in another patch rather than its own.
Abstract
Epidemic theory predicts that the vaccination threshold required to interrupt local transmission of an immunizing infection like measles depends only on the basic reproductive number ℛ0 and hence transmission rates. When the search for optimal strategies is expanded to incorporate economic constraints, the optimum for disease control in a single population is determined by relative costs of infection and control, rather than transmission rates. Adding a spatial dimension, which precludes local elimination unless it can be achieved globally, can reduce or increase optimal vaccination levels depending on the balance of costs and benefits. For weakly coupled populations, local optimal strategies agree with the global cost effective strategy; however, asymmetries in costs can lead to divergent control optima in more strongly coupled systems—in particular, strong regional differences in costs of vaccination can preclude local elimination even when elimination is locally optimal.
Under certain conditions, it is locally optimal to share vaccination resources with other populations.
Keywords
health economics,
transmission,
Vaccination
