In May 1985, the Pan American Health Organization launched an initiative to interrupt indigenous transmission of the wild poliovirus from the Western Hemisphere by the year 1990. The strategy to achieve this goal was based on the maintenance of high levels of immunity in the population at risk and the establishment of a surveillance system to detect polio cases and respond promptly with control measures. On 23 August 1991, a 2-year-old boy with acute flaccid paralysis due to wild poliovirus was detected in Junin, Peru, the last isolation of such a virus in the entire Western Hemisphere. In 1990, an International Commission for the Certification of Eradication of Poliomyelitis Eradication (ICCPE) was established by the Pan American Health Organization to eventually determine if transmission was interrupted. After 3 years of follow-up and review of surveillance data, the ICCPE declared that wild poliovirus transmission had been interrupted in the Americas.
In Finland paralytic poliomyelitis has disappeared after immunization programs carried out exclusively with inactivated poliovirus vaccine (IPV). A sharp decrease in the number of patients with poliomyelitis occurred after mass vaccination in 1960-1961, when 51% of the population had received the complete primary vaccination. Immunity is maintained by continuous vaccination of infants, whose vaccination rate is close to 98%. Intensive poliovirus surveillance in 1972-1974 revealed that dissemination of the virus has also virtually ceased. Serologic surveys indicate that greater than or equal to 90% of individuals older than 15 years of age possess antibodies to all viral types, but in the younger age groups the proportion with antibodies to types 1 and 3 is lower, a finding that is alarming, especially in the case of type 3. Revaccination of seronegative children and conscripts has induced rapid booster-like responses, indicating that fully vaccinated individuals, although without demonstrable antibodies, are protected against poliomyelitis. The new, improved IPV developed in Holland induces satisfactory antibody titers in all vaccinees, with two injections--or perhaps even one--leading to long-lasting immunity.
Since the mass vaccination in 1960, infants have been vaccinated systematically with inactivated polio vaccine. By school entry 97% of children have received complete primary vaccination. Since 1964 no case of poliomyelitis has been found in Finland. An intensified search for polioviruses among patients with polio-like diseases, among preschool children and in sewage did not reveal any polioviruses, giving evidence of their disappearance. Studies on immunity showed unexpectedly large numbers of preschool children without detectable antibodies to type 1 and especially to type 3. Their response to a booster dose revealed a secondary type reaction, indicating immunity. Thus, antibodies in low or even undetectable titres protect individuals from polio infection and furthermore may eliminate polio viruses from the country.
Since the launch of the Global Polio Eradication Initiative (GPEI) in 1988, knowledge as to the nature of circulating polioviruses and the challenges to their interruption has increased tremendously, particularly during the period 2000-2005. By January 2006, however, the systematic application of the standard polio eradication strategies, combined with recent refinements, had reduced the number of countries with ongoing transmission of indigenous wild polioviruses to just four (Nigeria, India, Pakistan, and Afghanistan), the lowest ever in history. In addition, only 8 of the 22 areas that had been re-infected by wild poliovirus in 2003-2005 still required large-scale 'mop-up' activities and circulating vaccine-derived poliovirus (cVDPV) outbreaks were being readily addressed. This progress, despite new challenges late in the GPEI, was greatly facilitated by a range of solutions that included two new monovalent oral polio vaccines (mOPVs), new and robust international standards for polio outbreak response, and renewed political commitment across the remaining infected countries.
In the first 4 months of 1974, 140 gauze pad samples of sewage collected in the Ottawa area were analysed by the BS-C-1 cell system for the presence of viruses pathogenic for humans. Viruses were isolated from 111 (79%) of the samples. Of the 72 (65%) isolates identified by serology and electron microscopic examination, 56 (78%) were reoviruses and 16 (22%), enteroviruses. The enterovirus isolates included one coxsackievirus B4, one vaccine strain of poliovirus type 3, nine vaccine strains of poliovirus type 1 and five strains of poliovirus type 1 that proved by serodifferentiation and temperature marker tests to be different from vaccine strains. The fact that these strains were present in the community sewage in readily detectable concentrations at a time when immunity against polioviruses is declining in such communities is a cause for concern.
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