Decision-making on the use of poliomyelitis vaccines in the WHO Expanded Immunization Programme, and particularly in the developing nations, needs to be based on an understanding of the epidemiology of poliomyelitis in different parts of the globe. Even with two safe and effective kinds of poliomyelitis vaccine available, poliomyelitis has by no means been eradicated from the world. In developed countries that are considered well-vaccinated, certain sectors of the population may be inadequately protected against risk of infection by indigenous or imported wild polioviruses. In developing nations that are in transition toward an epidemic phase of poliomyelitis, wild polioviruses will continue to be a threat until thorough immunization is established and maintained. Killed-virus poliomyelitis vaccines have proved to be effective in certain countries that have used them exclusively; these are small countries with excellent public health systems, where coverage by the killed vaccine has been wide and frequent. Live vaccines, administered to hundreds of millions of persons during the past decade, have also been remarkably safe and effective. However, in certain warm-climate countries induction of antibodies in a satisfactorily high proportion of vaccinees has been difficult to accomplish. The advantages and disadvantages of each kind of poliomyelitis vaccine need to be weighed with respect to the particular setting in which a vaccine has been or will be used.
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A serologic survey was made in 15 health unit areas, testing some 5000 individuals in the age groups 4 to 6, 11 to 13, 15 to 17 and 23 to 45 years. Two types of serious deficiency were found. Only 65% of children 4 to 6 years old had antibodies to all three types of poliovirus, the antibodies being due almost entirely to immunization with Salk vaccine. Even in children who had had six or more doses only 74% had antibodies to the three types. The high percentage of students 11 to 13 and 15 to 17 years old with poliovirus antibodies can be attributed largely to natural infection and to Sabin vaccine in the mass campaign of 1962, as well as to Salk vaccine. In children who had received Sabin vaccine as well as Salk vaccine a very high level of immunity was found. The immunity of the school-age population will decline to an insufficient level unless Sabin vaccine is used after immunization with Salk vaccine. Of children 4 to 6 years old 18% had no diphtheria antitoxin and 6% had no tetanus antitoxin. Even in those who had had six or more doses of the antigens 5% had no diphtheria antitoxin and 1 to 2% had no tetanus antitoxin. This apparently refractory state is probably due to the use of unadsorbed toxoids, and it is clear that adsorbed toxoids should be used. In the adults, diphtheria antitoxin was found in only 55% and tetanus antitoxin in only 38%.
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In 2010, a type 1 poliovirus outbreak in Congo with 445 lethal cases was caused by a virus that was neutralized by sera of German adults vaccinated with inactivated polio vaccine with a reduced efficiency. This seroprevalence study was done in two cohorts immunized with other vaccination schedules. Russian children aged 3-6 years immunized with a combination of inactivated and live polio vaccines were reasonably well protected against any wild type poliovirus 1, including the Congolese isolate. Adults aged 20-29 years immunized only with live vaccine were apparently protected against the vaccine strain (92% seropositive), but only 50% had detectable antibodies against the Congo-2010 isolate. Both waning immunity and serological divergence of the Congolese virus could contribute to this result.
Mass vaccination has led poliomyelitis to become a rare disease in a large part of the world, including Western Europe. However, in the past 20 years wild polioviruses imported from countries where polio is endemic have been responsible for outbreaks in otherwise polio-free European countries. We report on the characterization of poliovirus isolates from a large outbreak of poliomyelitis that occurred in Albania in 1996 and that also spread to the neighboring countries of Yugoslavia and Greece. The epidemics involved 145 subjects, mostly young adults, and caused persisting paralysis in 87 individuals and 16 deaths. The agent responsible for the outbreak was isolated from 74 patients and was identified as wild type 1 poliovirus by both immunological and molecular methods. Sequence analysis of the genome demonstrated the involvement of a single virus strain throughout the epidemics, and genotyping analysis showed 95% homology of the strain with a wild type 1 poliovirus strain isolated in Pakistan in 1995. Neutralization assays with both human sera and monoclonal antibodies were performed to analyze the antigenic structure of the epidemic strain, suggesting its peculiar antigenic characteristics. The presented data underline the current risks of outbreaks due to imported wild poliovirus and emphasize the need to improve vaccination efforts and also the need to implement surveillance in countries free of indigenous wild poliovirus.
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Virus isolated from an outbreak of poliomyelitis in Finland has been examined serologically and at the molecular level. The causative agent was an antigenically unusual strain of type 3 poliovirus, which was unrelated to the strains used to manufacture either live or killed poliovaccines. It is likely that the antigenic properties of the virus played a part in establishing a limited outbreak of poliomyelitis in a vaccinated population.
Antigenic properties of 128 clinical type 3 poliovirus isolates of the 1984 to 1985 Finland outbreak from 95 persons and 45 strains from sewage water specimens were evaluated using five neutralizing monoclonal antibodies (MAbs) directed against an antigenic site (designated site 1) on VP1 at amino acids 89 to 100. All five MAbs neutralized the type 3 poliovirus strains used in the vaccines, P3/Saukett and P3/Sabin, but none of them neutralized the prototype strain of the outbreak (P3/Finland/23127/84). Forty-six percent of the clinical isolates resembled the prototype strain (class A) while the rest of the isolates were neutralized by one or more of the MAbs (classes B to D). Although an antigenic drift from A to one of the other classes was observed in sequential specimens from several individuals, no clear-cut overall change in the class distribution was found within the 3 months time span of the outbreak. Homogeneous virus populations were isolated from the sewage specimens using a microtitre endpoint dilution method. The last positive sewage specimens which were obtained in January to February 1985 still had a majority of the class A strain. Some of the clinical isolates were also tested using MAbs directed against distinct antigenic sites. These studies showed that strains that gave the same pattern of reactivity with site 1 MAbs could be differentiated using antibodies directed against other sites. Fifteen strains belonging to different antigenic subclasses were subjected to partial RNA sequencing of the genome region coding for antigenic site 1. The antigenic variation was usually, but not always associated with corresponding amino acid substitutions in antigenic site 1. These results indicate that the antigenic sites of type 3 poliovirus vary extensively within a given outbreak and even during replication in a given host. This variation may have both pathogenetic and epidemiological significance.
A nationwide vaccination campaign with oral poliovirus vaccine was organized in Finland in 1985 to halt an outbreak of poliomyelitis. Immunocompromised persons and their household contacts were excluded from the oral poliovirus vaccine target group and given instead a dose of inactivated poliovirus vaccine. This gave us an opportunity to determine whether immunocompromised persons are protected from poliomyelitis during an outbreak and oral poliovirus campaign. Fourteen children, ages 3 to 17 years, with leukemia were given a booster dose of a novel high antigen content, trivalent inactivated poliovirus vaccine. All but two responded by an at least 4-fold increase in serum-neutralizing antibodies to at least one poliovirus serotype. These results indicate that children with acute lymphocytic leukemia in remission respond well to a booster dose of inactivated poliovirus vaccine. Antibody concentrations to the uncommon local epidemic strain of type 3 poliovirus remained, however, relatively low in most patients (median, 1:6) suggesting relatively impaired heterologous response to vaccination. Possible spread of live vaccine viruses to the inactivated poliovirus-vaccinated children and their close contacts was evaluated by examining weekly fecal specimens from 20 children and their 19 regular adult contacts for cytopathic viruses. No polioviruses were isolated from 224 specimens examined, indicating that this high risk population was well-protected from unintended exposure to live polioviruses.