International agreements for optimal disease control
Seminar Room 1, Newton Institute
AbstractOne of the key issues in the control of immunizing infections is determining the optimal level of vaccination in a population and achieving it. What is optimal for a whole population might not be best for an individual; and what is optimal for one country might not be optimal for their neighbours. This talk describes how the optimum level of vaccination results from interplay between epidemiological dynamics and the economic constraints that shape and influence control strategies on local, national and international levels.
From an epidemiological perspective alone, vaccination policies are guided by the basic reproductive number R0 - the average number of new infections caused by a single case in a wholly susceptible population. In order to locally interrupt transmission, vaccination coverage should be at or above the critical elimination threshold, 1 - 1/R0. However, when local economic constraints in the form of the relative costs of vaccination and infection are added to this picture, the optimal control level can range anywhere from no intervention to elimination; for a non-virulent pathogen, it may be optimal to sustain immunization well below the elimination threshold.
Turning to consider multiple countries connected by migration, the incentives of one country to invest in vaccination are additionally dependent on their neighbours' vaccination coverage and infection status. In the absence of regional or global bodies that can impose a universal vaccination strategy, human mobility could promote free-riding on each others' vaccination efforts, leading to a below-optimal coverage (surprisingly, at a higher overall cost).
The last part of this talk outlines a potential solution to this problem, specifically the use of coalition formation as a regional public health tool. Theory suggests that self-enforcing coalitions can lead to higher, more consistent and more uniform regional vaccination coverage even in the absence of global enforcement, but how do they became a reality?