Crude childhood vaccination coverage in West Africa: Trends and predictors of completeness [version 1; Referees: 1 approved, 3 approved with reservations]

Background: Africa has the lowest childhood vaccination coverage worldwide. If the full benefits of childhood vaccination programmes are to be enjoyed in sub-Saharan Africa, all countries need to improve on vaccine delivery to achieve and sustain high coverage. In this paper, we review trends in vaccination coverage, dropouts between vaccine doses and explored the country-specific predictors of complete vaccination in West Africa. Methods: We utilized datasets from the Demographic and Health Surveys Program, available for Benin, Burkina Faso, The Gambia, Ghana, Guinea, Cote d’Ivoire, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo, to obtain coverage for Bacillus Calmette-Guerin, polio, measles, and diphtheria, pertussis and tetanus (DPT) vaccines in children aged 12 – 23 months. We also calculated the DPT1-to-DPT3 and DPT1-to-measles dropouts, and proportions of the fully immunised child (FIC). Factors predictive of FIC were explored using Chi-squared tests and multivariable logistic regression. Results: Overall, there was a trend of increasing vaccination coverage. The proportion of FIC varied significantly by country (range 24.1-81.4%, mean 49%). DPT1-to-DPT3 dropout was high (range 5.1% -33.9%, mean 16.3%). Similarly, DPT1-measles dropout exceeded 10% in all but four countries. Although no single risk factor was consistently associated with FIC across these countries, maternal education, delivery in a health facility, possessing a vaccine card and a recent post delivery visit to a health facility were the key predictors of complete vaccination. Conclusions: The low numbers of fully immunised children and high dropout between vaccine doses highlights weaknesses and the need to strengthen the healthcare and routine immunization delivery systems in this region. Country-specific correlates of complete vaccination should be explored further to identify interventions required to increase vaccination coverage. Despite the promise of an increasing trend in vaccination coverage in West African countries, more effort is required to attain and maintain global vaccination coverage targets. This study utilized datasets from DHS conducted in 13 West African countries: Benin, Burkina Faso, Cote d’Ivoire, The Gambia, Ghana, Guinea, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo. DHS methodology encompasses a two-stage cluster sample design that produces unique, consistent, and nationally representative data that are comparable across countries 10. While these DHS datasets are not primarily carried out to collect vaccination data, they incorporate a questionnaire for women of reproductive age (15–49 years) for maternal and child health (including immunisation) in relation to all births within the preceding five years 5. DHS survey interviewers obtain immunization information from vaccine cards and/or mother’s/respondent’s recall. For countries with multiple datasets between 2000 and 2013, we assessed trends in vaccination coverage using their two most recent standard DHS datasets, as follows: Benin (2006 and 2011–12); Burkina Faso (2003 and 2010); Ghana (2003 and 2008); Guinea (2005 and 2012); Liberia (2007 and 2013); Mali (2006 and 2012–13); Niger (2006 and 2012); Nigeria (2008 and 2013); Senegal (2005 and 2010–11) and Sierra Leone (2008 and 2013). The rest of the analyses to calculate dropouts and determine the predictors of a FIC included countries with single datasets (Cote d’Ivoire 2011–12, The Gambia 2013, and Togo 2013–14) and the most recent dataset for those countries with multiple datasets. We followed the widely recommended strategy for measuring complete vaccination status by restricting our datasets to children aged 12–23 months and dropping all children that had passed away by the date of interviews 7, 11, 12. Our primary outcome was the fully immunised child (FIC). A FIC was defined as having received at birth or first contact, a dose of Bacille Calmette-Guérin vaccine (BCG), a 3-dose course of the diphtheria, pertussis and tetanus combination vaccine (DPT), and oral polio vaccine (OPV; given at 6, 10 and 14 weeks or at least four weeks apart) and a dose of measles-containing vaccine (MCV1; administered at 9 months), as reported by vaccine card or caregiver recall 9, 13. Other outcomes of interest in this study included access and utilization to immunization services. Good access was defined as having a DPT1 coverage of >80%, whereas a good utilization was defined as a DPT1-to-DPT3 dropout <10% 14. All statistical analyses were performed using STATA software, version 13.1 (StataCorp, Lakeway Drive, College Station, TX, USA). In descriptive analysis, we reported the proportions of FIC and those who received each vaccine dose by country, as well as the percentage DPT1-to-DPT3 and DPT1-to-MCV1 dropout 15. Chi-square tests were utilized in univariate analyses to examine associations between FIC and possible risk factors. The risk factors considered were: maternal age, maternal education, gender, religion, place of delivery, marital status, distance from home to nearest health facility, possession of a vaccine card, number of siblings, birth order, socio-economic status, rural or urban residence, and whether the child received a check-up within two months of birth 7, 13, 16– 21. Following this, we constructed multivariable logistic regression models within each country to examine the correlates of FIC. All factors identified at 10% significance (P-value <0.10) in univariate analysis were incorporated into the model. Before fitting the model, we assessed for potential collinearity using the Pearson’s R correlation coefficient (r > =0.8), and retained strongly correlated variables as suggested in the literature 22, 23. To account for the complex DHS survey design, the svyset command in STATA was used to apply inverse probability weights ( http://www.ats.ucla.edu/stat/stata/faq/svy_introsurvey.htm). Adjusted odds ratios (AORs) and 95% confidence intervals are reported at a 5% significance level. Ethical approval was not required for this study because it used anonymised DHS data. DHS surveys are conducted only after approvals have been given by the ICF International Institutional Review Board (IRB) and country IRBs for country-specific DHS survey protocols. In addition, written informed consent is obtained from each survey participant ( http://www.dhsprogram.com/What-We-Do/Protecting-the-Privacy-of-DHS-Survey-Respondents.cfm. The aggregate data utilised in this study was made freely available by DHS after after a simple registration process on their website ( http://www.dhsprogram.com/data/new-user-registration.cfm), which includes providing an explaination for the need for the datasets and planned analyses.