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ECONOMIC CONSIDERATIONS FOR THE ERADICATION ENDGAME

Tuesday, 27th of January 2015

ECONOMIC CONSIDERATIONS FOR THE ERADICATION ENDGAME

Scott Barrett

DOI: 10.1098/rstb.2012.0149Published 24 June 2013

Full text, with formulas, is at http://rstb.royalsocietypublishing.org/content/368/1623/20120149

Abstract

An infectious disease will be eradicated only if it is eliminated everywhere, including in the hardest-to-reach, most vaccine-wary communities. If eradication is successful, it promises a dividend in the form of avoided infections and vaccinations. However, success is never certain unless and until eradication is achieved, and claiming the dividend means bearing the possibly great risk of re-emergence. Economic analysis of eradication evaluates these risks and rewards relative to the alternative of optimal control, and also exposes the incentives for achieving and capitalizing on eradication. Eradication is a game, because some countries may be willing to eliminate the disease within their borders only if assured that all others will eliminate the disease within their borders. International financing is also a game, because each country would rather free ride than contribute. Finally, for diseases such as polio, capitalizing on eradication is a game, for should any country continue to vaccinate in the post-eradication era using the live-attenuated polio vaccine, the countries that stop vaccinating will be exposed to the risk of vaccine-derived polioviruses. In the framework developed in this paper, eradication is a seductive goal, its attainment fraught with peril.

1. Introduction

Eradication of a global scourge is an audacious undertaking. Its achievement depends on the cooperation of nearly every community in every country. It requires pushing a complex biological–social–political system into unchartered territory. It requires belief that the goal is achievable, even though success cannot be guaranteed. It requires trust in the people and organizations leading the effort. It requires patience. It requires resources. It requires luck. Unlike any other public health goal, it is intolerant of error. An eradication effort that reduces cases 99 per cent and no more fails to achieve its goal. Even before an eradication effort begins, attention must focus on how it will end.

If it ends successfully, then eradication can potentially save money as well as lives—money that can be spent on other good causes. Moreover, these dividends will be paid year after year, generation after generation. The rewards from eradication can be immense.

The risks can also be immense. Eradication may fail (previous efforts to eradicate hookworm, yellow fever, yaws and malaria all failed). If it succeeds, and we capitalize on its achievement by ceasing vaccination, then the world will be left more vulnerable than ever to a new outbreak. In terms of risks and rewards, few public policy goals can compare with eradication.

With so much at stake, economic analysis is critical, but many analyses of eradication rest on weak conceptual underpinnings (see [1]). First, some studies (examples include [2,3]) compare eradication with no control, or a similarly arbitrary alternative, when it should be compared with optimal control. Second, virtually all studies assume that eradication is certain to be achieved, when the (subjective) probability of success will always be smaller than one. Finally, very few studies incorporate post-eradication risks or the costs of mitigating these.

In this paper, I develop a framework for economic analysis of eradication, grounded in simple epidemiology. The framework exposes the tensions between private and public interests—tensions that can make elimination difficult to achieve. It assumes that the disease harms and is transmitted by humans, and that the pathogen is controlled, eliminated and possibly eradicated by means of a vaccine. I demonstrate its relevance for three cases: smallpox, poliomyelitis and measles.

Most analyses ask only if the economics of eradication are favourable overall. However, to succeed, pursuit of the goal must also be consonant with the self-interests of every state. Some states will attempt to eliminate a disease only if assured that all other states will eliminate the disease, making eradication a game. Other states will increase vaccination only if given assistance. The states that gain from eradication should be willing to pay, but each will prefer that others pay, making financing another game. Finally, the incentives to eradicate and to finance eradication depend ultimately on whether vaccination can cease should eradication succeed, for only then will eradication yield a dividend. In the case of polio, if just one state continues to vaccinate with the live-attenuated vaccine in the post-eradication era, then other states may continue to vaccinate to protect against the threat of circulating vaccine-derived polioviruses, preventing a dividend from being realized and making vaccination cessation another game. All of these games are critical and they are also interlinked. A weakness in any one game threatens the others. Eradication is a precarious enterprise.