|Polio - The Beginning of the End (WHO, 1997, 113 p.)|
A 13-member Global Commission has been appointed to certify the global eradication of polio. Its members were selected on the basis of their scientific expertise and objectivity. While none is working directly within the polio eradication initiative, all are eminent doctors, scientists, and academics working in related fields. The Commission members share responsibility for verifying that polio has been eradicated globally. In this, their scientific reputations - as well as the health of millions - are at stake.
Certification will be carried out on a regional basis by six Regional Commissions. At national level, each country is requested to establish a National Committee with responsibility for assessing and verifying polio surveillance data before their submission to the Regional Commission. Final certification will not be considered in any region until at least three years after the last virologically confirmed case of polio involving wild poliovirus. The Global Commission, which met for the first time in February 1995, has produced standard guidelines for data collection, drawn up a timetable for the certification process, and established the criteria on which certification will be based. It has been able to draw on the experience of the International Certification Commission on Polio Eradication in the Americas, which certified in August 1994 that polio had been eradicated from every country in the western hemisphere - three years after the last case occurred in Peru.
Surveillance for both acute flaccid paralysis cases and wild polio-viruses forms the basis of the documentation needed for certification. The Commission must be satisfied that, if polio cases had occurred, they would have been detected, reported, and rapidly and thoroughly investigated. Performance indicators for surveillance have been established to help confirm this. Where reports are not submitted, the reasons must be clearly documented and analysed. No grey areas will be accepted.
Surveillance for acute flaccid paralysis must meet four stringent criteria before certification can be considered: surveillance should be sensitive enough to detect at least one case of acute flaccid paralysis for every 100 000 children under 15; adequate stool samples should be collected from at least 80% of these cases; detailed investigation of suspected polio cases should include clinical, epidemiological, and virological examination as well as a follow-up examination for residual paralysis after 60 days; a final classification of the case should be made by a committee of experts on the basis of these examinations; and at least 80% of monthly surveillance reports (including zero reporting) should be submitted on time.
Polio network laboratories must undergo regular proficiency testing.
Virological surveillance is also tightly regulated. The results of virus isolation tests will only be accepted from network laboratories, and these laboratories must undergo regular proficiency testing. Specimen collection, transport, and testing procedures are monitored through the use of performance indicators and proficiency testing. Stool specimens from close contacts under the age of five may also need to be tested in some areas - particularly those with poor surveillance systems. After the last case of polio in the Americas in 1991, over 25 000 stool samples were collected from about 6000 paralysed children and their contacts over three years to test for the presence of wild poliovirus. Eradication could not be certified without the proof that no more indigenous polioviruses were circulating in the region.
Environmental testing for poliovirus through sampling sewage and waste water may only be feasible in countries with organized sewerage systems. However, the Global Commission decided that environmental sampling could be used to provide supporting evidence of the absence of wild poliovirus. Researchers are now trying to develop sensitive and practical sampling and detection methods that can be used even in countries with no organized sewerage system or sophisticated laboratories. In mid-1997, WHO launched a comparative study of poliovirus detection through existing surveillance systems and through environmental sampling.
When the global smallpox eradication programme was launched in 1967, there were an estimated 10-15 million cases of smallpox a year, although only 1% of them were ever reported. Of these, at least two million died and a further 100 000 were blinded by the disease. More than 10 million remained severely disfigured.
The global onslaught on smallpox ended in 1979 - two years after the last case involving naturally occurring wild virus was reported in the town of Merca in Somalia. On 22 October 1977, 23-year old Ali Maow Maalin developed smallpox - and survived. (The last two cases of smallpox occurred in Birmingham, England, in 1978, after the virus escaped from a laboratory.)
The 12-year smallpox eradication campaign and the global certification of the eradication of the disease in October 1979 established many of the basic principles now being used for the certification of the eradication of polio. In many ways variola (smallpox) virus was similar to poliovirus. It caused a disease that only affected humans, immunity was lifelong, there was no long-term carrier state, no animal or insect reservoir, and the disease could be prevented by a vaccine. But there were several very significant differences.
For a start, smallpox vaccine was thermostable and only a single dose was needed to produce immunity. Although the polio vaccine used has the advantage of oral administration, it is heat sensitive and children need four doses, preferably during their first year of life.
More importantly, although smallpox was a highly infectious disease, it did not involve symptomless infections, as polio does. Virtually every case of smallpox was clinically apparent. Infection with variola virus was highly visible, involving a characteristic rash that was easily recognized - even by a layman - and not likely to be confused with other diseases. Because of this, the smallpox eradication team was able to produce a smallpox recognition card that could be shown to people to help speed up the search for cases. Smallpox also left distinctive, permanent scars on the faces of as many as two thirds of its victims. During the certification stage, scar surveys of young children were carried out to confirm that variola virus was no longer in circulation. If it was, there would be evidence of recent cases among the youngest children.
Finding evidence of recent polio cases is far more difficult. Although polio paralysis is highly visible, some cases of polio can be confused with other forms of paralysis - even by expert neurologists. And while recent cases of polio paralysis indicate where polio is occurring, the absence of cases does not necessarily prove that poliovirus is no longer in circulation. Wild poliovirus can circulate "silently" - producing recognizable clinical disease (polio paralysis) in fewer than 1% of children infected. For every child who is paralysed by polio, about 200 other children will either appear well or have an illness not easily recognized as polio - despite being infected with poliovirus. As a result, exhaustive surveillance work is required to ensure that, if cases are occurring at a low level, they will be detected, and that wild poliovirus is not still circulating at a low level among healthy children.
In 1988, the World Health Assembly envisaged that polio eradication would be a gift from the 20th to the 21st century.
Photo: Liba Taylor