62. Control and Eradication

Abstract

Only one disease, smallpox, has been eradicated from the world, meaning the certified global absence of human cases and of any nonhuman reservoir, and the absolute control of any infectious source such as laboratories. Smallpox was a special case: it was limited to humans, it was controllable by a stable and long–lasting vaccine, and its eradication was economically beneficial to all countries. Even so, eradication efforts barely succeeded. The World Health Assembly has formally called for the eradication of only two other diseases—polio and dracunculiasis (guinea worm disease). Both campaigns reduced cases by 99 percent, but eradication in both cases is still uncertain. Polio spread again following interruption of vaccination in 2004, and contrary to initial expectations, vaccination will have to be continued afterwards if eradication is achieved. Dracunculiasis is much more limited geographically and less infectious, but remains a problem in several very poor countries, some undergoing continued armed conflict.

The alternative to eradication is control, achieved by means of: interventions—reduction of disease vectors, environmental measures, individual vaccination, chemotherapy, or chemoprophylaxis—to restrict the circulation of an infectious agent below the level due to spontaneous, individual protective behavior. Whether eradication is worth pursuing depends on the additional costs and benefits compared to an optimal level of control. The economics of polio eradication looks less favorable than originally expected, and a continued high level of control may be all that is feasible. Eradication of dracunculiasis looks somewhat more favorable, but depends on external assistance. Eradication is always a risky effort that may fail for scientific, financial, or organizational reasons. In contrast to control, which provides a local public good, eradication is a weakest–link global public good requiring extensive collaboration by all countries.