Achieving complete vaccination for children has been challenging in Nigeria. Yet, addressing Nigeria’s completeness of vaccination requires ethno-cultural diversity consideration rather than nationally population based. This study explored patterns and determinants of complete vaccination among children of Hausa/Fulani, Igbo and Yoruba, the predominant ethnicities in Nigeria. The study used a cross-sectional data involving 3980 children aged 12–23 months extracted from the 2018 Nigeria Demographic and Health Survey dataset. In this study, complete vaccination is defined as a child who received all recommended vaccinations. A generalized linear mixed model applied to clustered data was used for data analysis (α = 0.05). The prevalence of complete vaccinations was 56.3%, 40.8% and 18.2% among Igbo, Yoruba and Hausa/Fulani children, respectively. The likelihood of complete vaccination was higher among children who were of Igbo (aOR = 1.38; CI: 1.20–1.59) compared with Hausa/Fulani. Predictors of complete vaccination were maternal age-at-childbirth, education, prenatal-care attendant and place of delivery among Hausa/Fulani; place of residence and perceived access to self-medical help, among Igbo; while prenatal-care attendance, among Yoruba. The odds of complete vaccination were higher among Hausa/Fulani (aOR = 1.65; CI: 1.04–2.61), Igbo (aOR = 2.55; CI: 1.20–5.44) and Yoruba (aOR = 4.22; CI: 1.27–13.96) children from higher wealth-quintile households compared to those from poor households. There was evidence of variability in the likelihood of complete vaccination in all the ethnic groups. The Hausa/Fulani tribe had the lowest complete vaccination coverage for children aged 12–23 months. Context-specific program intervention to improve complete vaccination is needed to ensure that the SDG target for vaccination is met.
The present analysis was conducted using the 2018 Nigeria Demographic Health Survey (NDHS) data. The NDHS is a population-based cross-sectional design aimed at providing maternal and child health indicators to assist policymakers and programme managers in designing and evaluating programs and strategies for improving the health of the country’s population.9 Nigeria is the most populated country in Africa with the population figure of about 200 million, of whom 17% were under-five children in 2018. Administratively, Nigeria has 36 states including a Federal Capital Territory zoned into six geopolitical groups. Of over 250 ethnic compositions, Hausa/Fulani, Igbo and Yoruba are predominant. The six regions in Nigeria are mainly defined by these three ethnic groups. While the Yoruba and Igbo women predominantly have formal education, only a few of such women are found in Hausa/Fulani ethnic groups. The Hausa/Fulani women mostly belong to Islamic religion. Contrariwise, the Igbo and Yoruba women are mainly Christians. Two-stage cluster sampling technique was employed for the survey using the sampling frame containing the enumeration areas (EAs) of the 2006 Nigeria Population and Housing Census (NPHC). At the first stage, 1400 EAs (referred to as clusters) were selected as the primary sampling units; the second stage involved the selection of 40,427 households as the secondary units for the survey. The detailed description of the sampling design and strategies has been reported in the 2018 NDHS report.9 In the present study, data of children aged 12–23 months, who had valid information on the basic recommended vaccines, belonged to eligible women of childbearing age who were residents of the selected households within the clusters, and either of the Hausa/Fulani or Igbo or Yoruba tribes. Children with missing information or ‘don’t know’ records were excluded from the analysis. A total of 3980 met all these criteria. In this study, the term ‘cluster’ was used in DHS to describe the ‘neighborhood’ where children live. The outcome of interest was the complete vaccination status of children aged 12–23 months as at a year old. Going by WHO recommendations, a child who received one dose of Bacille Calmette–Guerin (BCG), one dose of measles, three doses of polio, and three doses of diphtheria, tetanus and pertussis (DPT) vaccines by the age of 12 months has a complete vaccination.9,16 Therefore, children who have been immunized with all these basic vaccines are deemed to have complete vaccinations – this is coded “1”; and “0” if otherwise. The key independent variable was ethnicity. The analysis was restricted to the three most prominent ethnic groups: Hausa/Fulani, Igbo and Yoruba in Nigeria.24 Other independent variables were included to define child/maternal, household and health characteristics according to empirical literature.25,26 These include child sex, birth order, maternal age-at-birth, employment, education, marital status, region, place of residence, religion, household wealth status, media exposure, health insurance coverage, health decision-involvement, perceived access to self-medical help, place of delivery and prenatal-care assistance. A media exposure variable was derived and classified as exposed if a household had access to at least one of radio, television or newspaper; otherwise, not exposed. The wealth index variable was derived from the generated weighted factor score using principal component analysis as contained in the recode file. These scores were categorized into low, middle, and high wealth quintiles. Health decision-involvement’s variable is premised on women’s ability to decide on personal health care, household purchases and visitation to relatives. These related variables are coded as 2 (if she decides alone), 1 (if joint decision) and 0 (if she took no part), respectively. The aggregated scores were classified as 0 (no involvement), 1–3 (low) and 4–6 (high). Similarly, perceived access to self-medical help’s variable is derived subject to a woman opinion on the following dichotomized variables: obtaining permission to visit a health facility, getting the required treatment fee, distance to a health facility, or being accompanied to the health facility – 0 score implied no problem; otherwise, the problem. Frequencies, percentages and charts were used as descriptive measures at the univariate stage. The chi-square test was used to assess the association between the outcome variable and the individual independent variables at the bivariate stage. Asides, both simple and multiple GLMMs with a binomial random distribution and logit link function are used to explore the predictors of children’s complete vaccination. As clustering of children’s complete vaccination may ensue if characteristics within clusters are alike, failure to account for such clustered or nested nature of the data often lead to biased parameter estimates of the fixed effects. The method also supports the dependence structure of data for units within these clusters and estimates the magnitude of such correlation after taking into consideration the inclusion of explanatory variables.27 An extension of generalized linear models is the GLMM that accounts for all contextual information. The model appropriately estimates fixed- and random-effects for nested data. In brief, the model is as follows: Let Yij be the complete vaccination status of ith child in the jth cluster defined as For EY=1/Xij,φj,εj=π, the GLMM can be described as follows: where π=Pr(Y=1/Xij,φj,εj) =eβpxijp+θrφrj+εj1+eβpxijp+θrφrj+εj p-variable is the level-1 denoted by xijp (which varies within and between clusters); r-variable is the level-2 denoted by φrj (varies only between clusters); and the random intercept is εj At the bivariate level, GLMM was used to identify the respective explanatory variable’s influence on child complete vaccination. Also, it was used to identify predictors of complete vaccinations among children aged 12–23 months using a 4-stage approach at the multivariate level for the pooled data. The adopted 4-stage random intercept was premised on the classification of explanatory variables such that models 1, 2 and 3, respectively, included variables to define child/maternal, household and health characteristics, irrespective of their significance status at the bivariate level. Thereafter, significant factors from models 1–3 were included in the final model 4. Also, correlates of children’s complete vaccinations peculiar to each of the ethnic groups were identified using the significant factors (p < .05) in any of the simple models for each of the ethnicity. The odds ratios (OR) including their CIs and the intra-neighborhood correlation coefficient (ICC) which quantifies the proportion of variance explained due to hierarchical data clustering effect are reported. In each of the models, ICC was computed using the estimated random intercept variance and ICC ≥ 2% is deemed to have a significant neighborhood effect which calls for a multilevel approach.28 Akaike Information Criteria (AIC) values are also reported for model comparison; the model with the least value was adjudged as being more adequate.29 All analyses were carried out at 5% level of significance, using STATA 14 SE (StataCorp LP, College Station, USA). Ethical approval for the parent study was obtained from the Nigeria National Ethics Committee. Informed consent and all other international ethical standards of confidentiality and anonymity were certified. The details of the ethical approval have been reported earlier.9 The Demographic and Health Surveys Program approved the utilization of the dataset for the present analysis.
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