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Background: Recent trends in global vaccination coverage have shown increases with most countries reaching 90% DTP3 coverage in 2008, although pockets of undervaccination continue to persist in parts of sub-Saharan Africa particularly in the urban slums. The objectives of this study were to determine the vaccination status of children aged between 12-23 months living in two slums of Nairobi and to identify the risk factors associated with incomplete vaccination. Methods: The study was carried out as part of a longitudinal Maternal and Child Health study undertaken in Korogocho and Viwandani slums of Nairobi. These slums host the Nairobi Urban Health and Demographic Surveillance System (NUHDSS) run by the African Population and Health Research Centre (APHRC). All women from the NUHDSS area who gave birth since September 2006 were enrolled in the project and administered a questionnaire which asked about the vaccination history of their children. For the purpose of this study, we used data from 1848 children aged 12-23 months who were expected to have received all the WHO-recommended vaccinations. The vaccination details were collected during the first visit about four months after birth with follow-up visits repeated thereafter at four month intervals. Full vaccination was defined as receiving all the basic childhood vaccinations by the end of 24 months of life, whereas up-to-date (UTD) vaccination referred to receipt of BCG, OPV 1-3, DTP 1-3, and measles vaccinations within the first 12 months of life. All vaccination data were obtained from vaccination cards which were sighted during the household visit as well as by recall from mothers. Multivariate models were used to identify the risk factors associated with incomplete vaccination. Results: Measles coverage was substantially lower than that for the other vaccines when determined using only vaccination cards or in addition to maternal recall. Up-to-date (UTD) coverage with all vaccinations at 12 months was 41.3% and 51.8% with and without the birth dose of OPV, respectively. Full vaccination coverage (57.5%) was higher than up-to-date coverage (51.8%) at 12 months overall, and in both slum settlements, using data from cards. Multivariate analysis showed that household assets and expenditure, ethnicity, place of delivery, mother’s level of education, age and parity were all predictors of full vaccination among children living in the slums. Conclusions: The findings show the extent to which children resident in slums are underserved with vaccination and indicate that service delivery of immunization services in the urban slums needs to be reassessed to ensure that all children are reached. © 2011 Mutua et al; licensee BioMed Central Ltd.
The study was carried out in two informal settlements of Nairobi (Viwandani and Korogocho) where the African Population and Health Research Centre (APHRC) runs a demographic surveillance system referred to as the Nairobi Urban Health and Demographic Surveillance System (NUHDSS). The NUHDSS has been in operation since 2002 and has about 60,000 registered inhabitants in nearly 20,000 households. These two densely populated slums, each comprising 7 villages, have high unemployment, poverty, crime, poor sanitation and generally poorer health indicators when compared to Nairobi as a whole [5]. The two communities however have notable differences: Viwandani is bordered by an industrial area and attracts migrant workers with relatively higher education levels, while the population in Korogocho is more stable and shows more co-residence of spouses. In addition, Korogocho has less disparity with regard to sex and age distribution of the population compared with Viwandani. Being illegal settlements, the slums are served with limited health services. There are no public health facilities within the slums but there are public health facilities in the neighboring communities where residents of the slums can access vaccination services: Four health facilities are located in the neighbourhood of Korogocho and two are close to Viwandani. Vaccination services are also offered in private and non-governmental health facilities within or near the slums. This study uses data from the Maternal and Child Health component of a broader project entitled “Urbanization, Poverty and Health Dynamics” being implemented in Korogocho and Viwandani. All women from the NUHDSS area who gave birth since September 2006 were enrolled in the project and administered a questionnaire which asked about the vaccination history of their children. For the purpose of this study, we used data on 1848 children aged 12-23 months who were expected to have received all the recommended vaccinations during the first 12 months after births. The vaccination details were collected during first visit about four months after birth with follow-up visits repeated thereafter at four month intervals. All vaccination data were obtained from vaccination cards which were sighted during the household visit, as well as by recall from mothers. Almost all of the children (99%) were said to have vaccination cards during the visits but only 88% (1848) of the cards were seen at the time of interview (Figure (Figure1).1). Data on the socio-demographic characteristics of the households were also collected from the NUHDSS census rounds. Derivation of the sample of children included in the study from the NUHDSS. We defined full vaccination status as receiving all the basic childhood vaccinations as recommended by WHO by the end of 24 months after birth. Vaccination status was considered UTD at 12 months if the child had received the following vaccinations in the first year of life: One dose of BCG received shortly after birth, three doses of triple vaccine for diphtheria, pertussis and tetanus (DTP) or pentavalent, three doses of polio (excluding OPV-0 given shortly after birth), received at 6, 10, and 14 weeks after birth respectively, and measles vaccinations at the age of 9 months. UTD vaccination coverage was determined for children after 3 months during which BCG, OPV 0,1 and 2, as well as DTP 1 and 2 would have been administered. Some children received polio vaccine at birth and, therefore the analyses were repeated with full vaccination including OPV-0. Analysis was conducted only for children aged 12-23 using data on their vaccination status obtained within the first 24 months after birth. The household assets index was constructed using the principal component analysis (PCA). The assets index was derived from different assets owned by the household, both within the dwelling structure and elsewhere. These included motor vehicle, motorcycle, cooking stove, TV, refrigerator, and phone. The monthly expenditure was computed by dividing the monthly household expenditure by the equivalent household size, taking a child to be equivalent of half an adult. The poverty variables were computed at the household level and averaged for the village within which the households are located. The mean village poverty scores were then assigned to all the households in the respective villages and used as covariates in the modeling. Nine covariates were included in the analysis: sex of child, maternal education (none, primary, and secondary or higher), maternal age at index child’s birth (<20, 20-24, 25-29, 30+), parity (1, 2, and 3+), place of delivery (home or health facility), ethnicity (Kikuyu, Luhya, Luo, Kamba and Others), antenatal care (no ANC, seen a doctor, seen a nurse), birth weight (less than 2.5 kg, 2.5 kg or greater), postnatal care (no postnatal, postnatal care) and measures of poverty. Descriptive analysis was used to show the characteristics of the participants in the study and the extent of coverage for specific, UTD and full vaccination. A bivariate model was fitted for all covariates and those with a p value of less than 0.25 were included in the multivariate analyses. Multivariate models were used to identify the risk factors associated with incomplete vaccination in the study settlements. The poverty variables were computed for each village and a multilevel (random intercept model) technique was used to account for these village level factors [11]. Due to multi-dimensionality of poverty measurements, we fitted separate models to assess the effects of poverty. All models were fitted with the STATA "xtlogit" or "xtmelogit" command using verified immunization status data from vaccination cards. The conduct of the Urbanization, Poverty and Health Dynamics programme of research was approved by the Ethical Review Board of the Kenya Medical Research Institute (KEMRI). The field workers were trained in research ethics and obtained informed consent from all respondents in the Maternal and Child Health project. The NUHDSS has also been approved by KEMRI's Ethical Review Board. Verbal consent is usually obtained from all respondents.
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