Eradication

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Control, whether by vaccination alone or by vaccination plus the various other methods aimed at lessening the chances of infection, is an ongoing process, which must be maintained indefinitely. If a disease could be eradicated, so that the causative agent was no longer present anywhere in the world, except possibly in microbiologically and militarily secure laboratories, control of that disease would no longer be required. The term elimination is used for the interruption of transmission within a country or region, a situation that does not exclude the importation of infection from outside; eradication means elimination from the world.

So far, global eradication has been achieved for only one disease, smallpox, the last naturally occurring case of which was reported in Somalia in October 1977. Smallpox eradication was achieved by an intensive effort that involved a high level of international cooperation and utilized a potent and very stable vaccine that was easy to administer. However, mass vaccination alone could not have achieved eradication of the disease from the densely populated tropical countries where it remained endemic in the 1970s, because it was impossible to achieve the necessary very high level of vaccine coverage. The effective strategy was to combine vaccination with surveillance and containment, by which cases were actively sought out, isolated, and their contacts vaccinated, first in the household and then at increasing distances from the index case.

The global smallpox eradication campaign was a highly cost-effective operation. The expenditure by the World Health Organization between 1967 and 1979 was $81 million, to which could be added about $32 million in bilateral aid contributions and some $200 million in expenditures by the endemic countries involved in the campaign. Against this expenditure of about $313 million over the 11 years of the campaign could be set an annual global expenditure of about $1000 million for vaccination, airport inspections, etc., made necessary by the existence of smallpox. This equation takes no account of the deaths, misery, and costs of smallpox itself, or of the complications of vaccination.

The achievement of global eradication of smallpox gave rise to discussions as Lo whether any other diseases could be eradicated worldwide. International conferences were held to discuss two other viral diseases, namely, measles and poliomyelitis. The biological characteristics of the three diseases that affect the ease of eradication are set out in Table 15-3. These diseases share several essentia) characteristics: (1) no animal reservoir, (2) lack of recurrent infectivity, (3) one or few stable serotypes, and (4) an effective vaccine. However, some features that were very important in the eradication of smallpox from tropical countries, notably the lack of infectivity in the prodromal stage, which made surveillance and containment possible, are lacking in measles, whereas the preponderance of subclinical infections in poliomyelitis renders its eradication more difficult. In addition to the biological properties of smallpox being particularly favorable, there were strong financial incentives for the industrialized countries to promote the global eradication of smallpox, because of the costs associated with vaccination of international travelers, port inspections, etc. However, in contrast to their limited participation in the smallpox eradication campaign, UNICEF and other major sources of international funds have not only provided solid financial support for the EPI since 1985, but, heartened by the excellent results obtained with the reduction of poliomyelitis, have expressed great interest in the eradication of this disease.

In 1988 the WHO, UNICEF, and some other organizations agreed on joint activity to facilitate immunization against poliomyelitis, and in May 1988 the World Health Assembly voted to commit the WHO to global eradication of

Table 15-3

Comparison of Features Influencing the Feasibility of Eradication of Measles and Poliomyelitis, Compared with Smallpox, in Which All Features Were Favorable

Table 15-3

Comparison of Features Influencing the Feasibility of Eradication of Measles and Poliomyelitis, Compared with Smallpox, in Which All Features Were Favorable

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