ABSTRACT
Introduction: This study reviewed the epidemiological trends of poliomyelitis from 1946 to 2010, and the impact of the national immunisation programme in raising the population herd immunity against poliovirus. We also traced the efforts Singapore has made to achieve certification of poliomyelitis eradication by the World Health Organisation.
Materials and Methods: Epidemiological data on all reported cases of poliomyelitis were obtained from the Communicable Diseases Division of the Ministry of Health as well as historical records. Coverage of the childhood immunisation programme against poliomyelitis was based on the immunisation data maintained by the National Immunisation Registry, Health Promotion Board. To assess the herd immunity of the population against poliovirus, 6 serological surveys were conducted in 1962, 1978, 1982 to 1984, 1989, 1993 and from 2008 to 2010. Results: Singapore was among the first countries in the world to introduce live oral poliovirus vaccine (OPV) on a mass scale in 1958. With the comprehensive coverage of the national childhood immunisation programme, the incidence of paralytic poliomyelitis declined from 74 cases in 1963 to 5 cases from 1971 to 1973. The immunisation coverage for infants, preschool and primary school children has been maintained at 92% to 97% over the past decade. No indigenous poliomyelitis case had been reported since 1978 and all cases reported subsequently were imported. Conclusion: Singapore was certified poliomyelitis free along with the rest of the Western Pacific Region in 2000 after fulfilling all criteria for poliomyelitis eradication, including the establishment of a robust acute flaccid paralysis surveillance system. However, post-certification challenges remain, with the risk of wild poliovirus importation. Furthermore, it is timely to consider the replacement of OPV with the inactivated poliovirus vaccine in Singapore’s national immunisation programme given the risk of vaccine-associated paralytic poliomyelitis and circulating vaccine-derived poliovirusesParalytic poliomyelitis used to be a common childhood disease in Singapore. It was recognised as a major public health problem in the immediate post World War II period. The epidemiological pattern was that of an endemic disease with periodic epidemics, indicating transition from the endemic behaviour characteristic of countries with low levels of environmental sanitation, towards the epidemic behaviour characteristic of countries with improved hygiene standards. There was no seasonal pattern; cases occurred throughout the year, with epidemics recorded in 1946, 1948 and the end of 1950 and beginning of 1951. Age-specific incidence showed that children below the age of 5 years were most at risk, particularly those between 6 months and 2 years of age. Laboratory investigations showed that poliovirus type 1 was responsible for the majority of cases and for the epidemic waves; poliovirus type 3 was of minor importance, while poliovirus type 2 relatively unimportant.
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