Cluster survey evaluation of coverage and risk factors for failure to be immunized during the 1995 National Immunization Days in Egypt.
BACKGROUND: In 1995, Egypt continued to experience endemic wild poliovirus transmission despite achieving high routine immunization coverage with at least three doses of oral poliovirus vaccine (OPV3) and implementing National Immunization Days (NIDs) annually for several years. METHODS: Parents of 4188 children in 3216 households throughout Egypt were surveyed after the second round of the 1995 NIDs. RESULTS: Nationwide, 74% of children are estimated to have received both NID doses, 17% one NID dose, and 9% neither NID dose. Previously unimmunized (47%) or partially immunized (64%) children were less likely to receive two NID doses of OPV than were fully immunized children (76%) (P < 0.001). Other risk factors nationwide for failure to receive NID OPV included distance from residence to nearest NID site >10 minute walk (P < 0.001), not being informed about the NID at least one day in advance (P < 0.001), and residing in a household which does not watch television (P < 0.001). Based on these findings, subsequent NIDs in Egypt were modified to improve coverage, which has resulted in a marked decrease in the incidence of paralytic poliomyelitis in Egypt. CONCLUSIONS: In selected situations, surveys can provide important information that is useful for planning future NIDs. (+info)
Since the 1988 World Health Assembly resolution to eradicate poliomyelitis by 2000, polio cases reported globally have decreased by approximately 85%. Despite a strong commitment to polio eradication, polio remains endemic in Pakistan. In 1997, Pakistan reported 1147 polio cases, representing widespread poliovirus circulation nationally and constituting 22% of cases reported worldwide. However, surveillance and laboratory data from 1998 indicate that previous widespread poliovirus circulation was geographically localized for the first time. This report describes polio eradication activities in Pakistan, including the impact of routine and supplementary vaccination on polio incidence. (+info)
Wild poliovirus circulation among healthy children immunized with oral polio vaccine in Antananarivo, Madagascar.
From July 1995 to December 1996, 3185 stool specimens from healthy children aged 6-59 months attending 6 dispensaries in the Antananarivo area were examined for poliovirus. The children had been routinely immunized according to the Expanded Programme on Immunization (EPI) schedule and received the last dose of oral polio vaccine (OPV) more than 1 month before stool collection. 99.4% of the children were immunized with at least 3 doses of OPV. HEp-2 cell culture revealed virus infections in 192 stools (6.0%), including 9 poliovirus (0.3%) and 183 nonpolio enterovirus isolates (5.7%). Infections occurred throughout the year, but incidence was higher during the hot and rainy season (P=0.01). Using a neutralization test with monoclonal antibodies and PCR-RFLP in two genomic regions coding for the VP1 capsid and RNA polymerase, 4 wild polioviruses (3 type 1 and 1 type 3) and 5 vaccine-related polioviruses (2 Sabin 1-like variants, 1 Sabin 2-like and 2 Sabin 3-like) strains were identified. The wild polioviruses were isolated at the beginning and the end of the dry season. Similar RFLP patterns were observed for the 3 wild type 1 polioviruses. Comparison of partial genomic sequences in the VP1/2 A region of 1 of the wild type 1 isolates with 2 wild type strains isolated in Antananarivo in 1992 and 1993 showed a divergence of at least 10% between the strains, suggesting at least two different pathways of transmission during this period. Our findings demonstrate that immunization with 3 doses of OPV did not prevent intestinal carriage of wild poliovirus strains, and that there is a risk of wild poliovirus transmission to susceptible children in the area. Multiple strategies are required to improve immunization coverage in Madagascar. (+info)
A Sabin vaccine-derived field isolate of poliovirus type 1 displaying aberrant phenotypic and genetic features, including a deletion in antigenic site 1.
Poliovirus strains derived from the oral poliovirus vaccine (Sabin) can be differentiated from wild-type poliovirus by tests based on either immunological or genetic properties of the strains. The characterization of a recently identified poliovirus type 1 isolate with exceptional properties is described. Initial phenotypic analysis of the virus by use of polyclonal absorbed antisera suggested a wild-type character. However, the different genomic analyses all confirmed the Sabin-derived character of the virus. All 17 plaques isolated from the strain shared these properties, thus excluding the possibility of a mixture of a wild-type and a Sabin-derived strain. To elucidate the properties of this virus further, the nucleotide sequences of the P1 region and most of the 5' non-coding region were established. Although the nucleotide identity with Sabin 1 was more than 99.4%, mutations were observed in regions encoding three major antigenic sites; the deduced amino acid substitutions confirmed the aberrant results of micro-neutralization assays with site-specific monoclonal antibodies. The most striking feature was the existence of a hexanucleotide deletion in the VP1 gene, which gave rise to a two amino acid deletion in the BC loop. In spite of these antigenic changes, the strain was readily serotyped as poliovirus type 1 under standard conditions. Likewise, replication of the virus under cell culture conditions was not affected by these mutations or by the deletion. Standard polio vaccination protects against this aberrant virus, and its epidemiological significance remains open. (+info)
Progress toward poliomyelitis eradication--South East Asia Region, 1997-1998.
In 1988, the World Health Assembly resolved to eradicate poliomyelitis by 2000. To achieve this goal, in 1994 World Health Organization (WHO) South East Asia Region (SEAR) member countries accelerated implementation of polio eradication strategies. In 1994, Thailand became the region's first country to initiate National Immunization Days (NIDs), followed by Bangladesh, Bhutan, India, Indonesia, and Sri Lanka (1995); Myanmar and Nepal (1996); and Democratic People's Republic (DPR) of Korea and Maldives (1997). This report summarizes the progress in achieving routine and supplemental vaccination coverage and surveillance for cases of acute flaccid paralysis (AFP) and the impact of these activities on polio eradication in the region. (+info)
In 1988, the World Health Assembly resolved to eradicate poliomyelitis globally by 2000. In the African Region of the World Health Organization (WHO), eradication efforts were accelerated following supporting resolutions by WHO's Regional Committee for Africa in 1995 and the Organization of African Unity in 1996. Nigeria, the most populous country in Africa and part of a densely populated West African area extending from Nigeria to Cote D'Ivoire, is critically important to the global polio eradication initiative. This report summarizes 1) the success of National Immunization Days (NIDs); 2) the establishment of acute flaccid paralysis (AFP) surveillance; and 3) accelerated efforts to meet the 2000 target, including mopping-up planned for later in 1999. (+info)
Mutations in Sabin 2 strain of poliovirus and stability of attenuation phenotype.
In this study, we attempted to identify the molecular determinants in the genome of the attenuated Sabin 2 vaccine strain of poliovirus that may change during vaccine production and result in an increase in monkey neurovirulence. An extensive search for suitable vaccine lots identified six batches that had failed the monkey neurovirulence test (MNVT). On repeated tests, these batches were found to have acceptable levels of monkey neurovirulence. One of the batches was additionally passaged six times under conditions used in vaccine production, and the resulting high-passage sample was screened for the presence of mutations and tested in monkeys. In addition to the previously described A --> G reversion at nucleotide 481, high-passage stock also contained a mutation in the VP1-coding region (3364 = G --> A) that consistently accumulated in the course of passaging. However, despite the presence of substantial amounts of these mutations, high-passage stock passed the MNVT. Replication of Sabin 2 poliovirus in the central nervous system of transgenic mice susceptible to poliovirus or in cultures of mouse cells, resulted in another mutation (3363 = A --> G). Even though its presence correlated with paralysis in mice, the introduction of 3363-G into the Sabin 2 genome did not increase neurovirulence of the virus. Previous studies identified the 481-G mutation as an important determinant of monkey neurovirulence. We prepared virus samples with varying amounts of genetically defined single mutants at this nucleotide and tested them in monkeys. The results demonstrated that even a 100% substitution at this site introduced into Sabin 2 strain did not increase monkey neurovirulence. The determination of the nucleotide sequence of an alternative strain used for the production of type 2 OPV (Chung 2) showed that it contained 100% of the wild-type 481-G but possessed an extremely low level of neurovirulence. These results demonstrate the remarkable stability of the attenuated phenotype of the Sabin 2 strain and show that (1) no batch of OPV 2 has ever repeatedly failed the MNVT, (2) growing the virus beyond the passage level allowed in vaccine production did not result in increased neurovirulence in monkeys, (3) a test for neurovirulence in transgenic mice may be more sensitive than the MNVT, and (4) determination of the mutational profile of vaccine batches detects inconsistencies in vaccine manufacturing processing that would not be detected by the MNVT. (+info)
Progress toward global poliomyelitis eradication--1997-1998.
In 1988, the World Health Assembly resolved to eradicate poliomyelitis globally by 2000. Since then, substantial progress has been reported by all countries where polio is endemic in implementing the recommended polio eradication strategies (i.e., achieving and maintaining high routine coverage with oral poliovirus vaccine [OPV]; conducting National Immunization Days [NIDs] to rapidly decrease poliovirus circulation; establishing sensitive surveillance systems for polio cases and poliovirus; and carrying out mopping-up vaccination activities to eliminate the remaining reservoirs of poliovirus transmission). Although much progress has been made in many countries, substantial obstacles remain, particularly in 14 priority countries (i.e., global reservoir countries or countries with ongoing armed internal strife or civil war). This report updates progress during 1998 toward the global eradication target and describes accelerated activities to achieve the 2000 goal. (+info)