The aim of this work was to study the state of immunity in children immunized with liquid poliomyelitis vaccine. During 1976-1981 the intensity of immunity to poliomyelitis in 653 children aged 1-3 years was studied. The study showed that at the period when liquid poliomyelitis vaccine was used the share immune to polioviruses, types 1 and 2, constituted 89.4% and 98.0%, respectively, as compared with 67.0% and 68.0% at the period when sugar-coated live dried poliomyelitis vaccine was administered. Changes in such epidemiological characteristics, as the percentage of persons with antibodies to poliovirus, were particularly essential in the age group of 1-2 years. In 1979 persons with antibodies to type 1 poliovirus constituted 94.0% as compared with 44.0% in 1976, while the percentage of persons found to be seronegative in respect of antibodies to polioviruses, types 1, 2 and 3, decreased 5-7 times. The quality of immunization carried out at the period, when liquid poliomyelitis vaccine was used, was shown to influence the size of the immune share, while having no effect on the geometric mean of the titer of antibodies to polioviruses.
A Sabin 3/Sabin 2/Sabin 3 (S3/2/3) intertypic recombinant poliovirus was isolated from a faecal specimen from a 2-year-old healthy boy approximately 12 weeks after administration of oral poliovirus vaccine. The first recombination junction was in the genomic region encoding the VP1 capsid protein between nucleotide positions 3274 and 3285 (numbering according to Sabin 3) and the second was in the RNA polymerase region (nucleotide positions 6824 and 6825). The recombination had introduced six Sabin 2-derived amino acids into the Sabin 3 capsid environment in the carboxyl terminus of VP1. The complete genome of the recombinant virus differed from corresponding parental Sabin strains at 33 nucleotide positions, nine of them resulting in an amino acid substitution. Four substitutions were in the capsid proteins and five were in the region encoding the non-structural proteins. One amino acid was changed in the antigenic site 2B and two in site 3B. In addition, the whole antigenic site 3A was replaced by Sabin 2-specific amino acids, but the antigenic characteristics of the S3/2/3 did not show type 2-specific features. Neutralizing antibody titres in sera from Finnish children immunized with the inactivated poliovirus vaccine were not lower against the recombinant virus than against Sabin 3. Our results suggest that the chimeric virus was most likely generated by recombination events in the vaccinee, rather than representing progeny of circulating vaccine-derived virus.
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.
Immune status to polioviruses in the child population of Romania between 2002-2005 as indicated by serological investigation in cases of acute flaccid paralysis (AFP) and facial paralysis (FP) and its use as a "national reference value" to evaluate the vaccination coverage in particular groups of healthy children.
Although the European region is polio free since 2002, the risk of importation from endemic regions remains present and a high level of population immunity must be maintained. In Romania during the period 2002-2005, 101 FP cases, 91 AFP cases and 29 healthy contacts (living in groups with low social and sanitary status, relatively low vaccination coverage named "at risk") could have been investigated serologically. Antibody prevalences for poliovirus types 1, 2, and 3 were: 97.2%, 98% and 81.2% for FP cases; 96.7%, 94.5% and 85.7% for AFP cases, and 85.7%, 82.1% and 53% for the group of healthy children at risk. The risk of the emergence and spread of cVDPVs remains present especially in "at risk" groups with the gaps in immunity, even in countries where indigenous wild polioviruses have already been eradicated.
The study of the state of herd immunity among the children of Kharkov, carried out in 1980-1981, has revealed different immunity levels in children of different age. The conclusion has been made that the constant control of the state of immunity to 3 types of poliovirus is necessary, especially in infants and in school children, as well as in those not attending children's institutions.
Assessment of immunity to poliomyelitis in adults from 8 towns of Moscow region was conducted. Low levels of population immunity against some serotypes of poliovirus in several towns have been found. At the same time, these levels were high and very high in other towns. Measurement of levels of strain-specific antibodies to vaccine and wild polioviruses demonstrated wide circulation of wild polioviruses during past decades which had significant influence on formation of immunity. Substantial number of non-immune adults represents favorable conditions for circulation of vaccine polioviruses after cessation of vaccination, which, in its turn, could result in reestablishment of their neurovirulent properties and subsequent reemergence of poliomyelitis.