Tracking coverage, dropout and multidimensional equity gaps in immunisation systems in West Africa, 2000-2017

Background Several West African countries are unlikely to achieve the recommended Global Vaccine Action Plan (GVAP) immunisation coverage and dropout targets in a landscape beset with entrenched intra-country equity gaps in immunisation. Our aim was to assess and compare the immunisation coverage, dropout and equity gaps across 15 West African countries between 2000 and 2017. Methods We compared Bacille Calmette Guerin (BCG) and the third dose of diphtheria-tetanus-pertussis (DTP3) containing vaccine coverage between 2000 and 2017 using the WHO and Unicef Estimates of National Immunisation Coverage for 15 West African countries. Estimated subregional median and weighted average coverages, and dropout (DTP1-DTP3) were tracked against the GVAP targets of ≥90% coverage (BCG and DTP3), and ≤10% dropouts. Equity gaps in immunisation were assessed using the latest disaggregated national health survey immunisation data. Results The weighted average subregional BCG coverage was 60.7% in 2000, peaked at 83.2% in 2009 and was 65.7% in 2017. The weighted average DTP3 coverage was 42.3% in 2000, peaked at 70.3% in 2009 and was 61.5% in 2017. As of 2017, 46.7% of countries (7/15) had met the GVAP targets on DTP3 coverage. Average weighted subregional immunisation dropouts consistently reduced from 16.4% in 2000 to 7.4% in 2017, meeting the GVAP target in 2008. In most countries, inequalities in BCG, and DTP3 coverage and dropouts were mainly related to equity gaps of more than 20% points between the wealthiest and the poorest, high coverage regions and low coverage regions, and between children of mothers with at least secondary education and those with no formal education. A child’s sex and place of residence (urban or rural) minimally determined equity gaps. Conclusions The West African subregion made progress between 2000 and 2017 in ensuring that its children utilised immunisation services, however, wide equity gaps persist.

This paper set out to analyse the immunisation system performance between 2000 and 2017 across 15 West African countries whose combined estimated population in 2017 was about 372 million.11 In 2017, the countries had an estimated total birth cohort and surviving infant population of 13 921 000 and 13 111 000, respectively (figure 1).12 TreeMap showing the distribution of the 13,111,000 estimated surviving infants’ population across West Africa in 2017. (Source: Developed by authors based on UN population estimates of surviving infants for 2017). *Cabo Verde. The West Africa subregion has a regional alliance, the Economic Community of West African States (ECOWAS) aimed at promoting integration in all fields of activity, including the health of the constituting countries. The West African Health Organisation (WAHO) is a specialised institution of ECOWAS responsible for health-related issues in the subregion. The ECOWAS is made up of 15-member countries including Benin, Burkina Faso, Cabo Verde, Cote d’ Ivoire, The Gambia, Ghana, Guinea, Guinea Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo who have cultural and geopolitical ties, and shared economic interest.11 Ten of these fifteen countries were low-income countries with Gross National Income (GNI) per capita of $995 or less, whereas Cabo Verde, Cote d’Ivoire, Ghana, Nigeria and Senegal were lower-middle-income countries with GNI per capita of between $996 and 3895 based on the 2017 World Bank fiscal year classification.13 We examined publicly available secondary data on Bacille Calmette Guerin (BCG), and DTP3 immunisation coverage, DTP1–DTP3 dropout rates and intra-country equity gaps, between 2010 and 2017 across 15 ECOWAS West African countries. This was an analysis of publicly available secondary data and did not involve primary patients or study participants in the development of the study question, study design or conduct of the study. As this study was based purely on secondary analysis of data and involved no primary data collection involving patients or vulnerable groups, ethical approval was neither required nor sought. The ethical procedures for the secondary data used were the responsibilities of the institutions that commissioned, funded or managed the surveys utilised. The protocol for Demographic Health Survey (DHS) was reviewed and approved by ICF Institutional Review Board, and each host country’s ethics board prior to the commencement of the surveys.14 The Multiple Indicator Cluster Survey (MICS) survey protocols were reviewed by country-level ethics review boards and approved according to the laws in each host country.15 Additionally, DHS and MICS reports that survey respondents gave written informed consent before participation. Immunisation systems performance is measured via multiple dimensions, including immunisation coverage, immunisation dropout, equity of coverage, the completeness of vaccines in the national schedule compared with recommended vaccines and other administrative indicators.16 In this paper, we measured immunisation coverage using BCG immunisation coverage and DTP3 immunisation coverage. Immunisation dropout was assessed by measuring the DTP1 to DTP3 dropout rates. To evaluate levels of inequality in immunisation coverage, we stratified the immunisation coverage by socioeconomic and geographic determinants of inequality. These include (i) child’s sex; (ii) location of residence; (iii) maternal education; (iv) regions within a country and (v) wealth quintile according to the framework of the WHO Commission on Social Determinants of Health.17 Although the framework considers other dimensions such as ethnicity, migration status and other intermediate determinants, we were not able to include these indicators in the analyses because they are not routinely captured in national survey data. National BCG and DTP3 vaccination coverage estimates were obtained from country-specific WHO and Unicef Estimates of National Immunisation Coverage (WUENIC) data for all 15 countries.18 The data extracted covered a period beginning from one-decade pre-GVAP (2000) up until the most current country-specific data as of December 2018. National and regional estimates of birth cohort and the number of surviving infants were computed using the UN Population Division population estimates, 2017 revision, which are comparable to the estimates available in WUENIC databases.12 To determine equity gaps in vaccination coverage, we searched the publicly available UNICEF-supported MICS and the USAID-supported DHS databases for each country’s most recent final report of either household surveys as of December 2018.19 20 The MICS and DHS are nationally representative, large-scale and standardised household surveys, whose methodologies allow for direct comparisons of their data. They collect and report disaggregated health data, including immunisation coverages by several socioeconomic or geographical determinants of inequality including wealth quintile, maternal education, location of residence, regions within a country and child’s sex.21 The detailed methodologies of MICS and DHS are described elsewhere.21 The data generated after abstraction from the various data sources were entered into and analysed descriptively using Microsoft Excel (2016). BCG immunisation coverage was estimated as the percentage of children 12–23 months in each country who had received BCG.16 We calculated the median, and the average subregional coverage weighted by each country’s corresponding annual birth cohort population from 2000 to 2017. BCG coverage was selected as an indicator as it is considered a key determinant of access to health services.22 Furthermore, we illustrated the highest and lowest BCG immunisation coverage in the subregion for the corresponding year by creating two trend lines representing the country with the highest and lowest BCG coverage from 2000 to 2017. To track progress in BCG immunisation coverage, the GVAP recommended minimum coverage target of 90% was used as the reference standard.8 The DTP3 immunisation coverage indicator was defined as the percentage of children aged 12–23 months who had received DTP3.16 Similar to estimating BCG immunisation coverage, we estimated the subregional DTP3 coverage trends from 2000 to 2017 by calculating and reporting the median, and average coverage weighted by each country’s corresponding annual surviving infant population. The countries with highest and lowest coverages for each corresponding year were illustrated using different trend lines. To track progress in DTP3 immunisation coverage, the GVAP recommended minimum DTP3 coverage target of 90% was used as the reference standard.8 We determined immunisation dropout rate for each country by calculating the proportion of children who dropped out from the immunisation system between DTP1 and DTP3,22 estimated by calculating the percentage coverage of DTP1 minus DTP3 for each country per year from WUENIC data.18 Similarly, we reported trends per country from 2000 to 2017, and illustrated the median and weighted average subregional trend in immunisation dropout, and the corresponding highest and lowest vaccine dropout representing the country with the highest and lowest dropout rates. To track progress in immunisation dropout, the GVAP recommended maximum dropout rate of 10% was used as the reference standard.8 Because the analysis considered West Africa as a single unit, we further highlighted the ‘hotspot’ countries where unvaccinated children lived in the subregion. We estimated the absolute number of unvaccinated children as the proportion of the 2017 country-specific number of surviving infants (number of children eligible for DTP3 vaccination) who did not receive DTP3 in 2017. We illustrated and compared this in relation to each country’s overall DTP3 coverage for the same year using a bubble map. We estimated the most recent situation of intra-country inequality in BCG and DTP3 coverage, and immunisation dropout using a single summary measure of difference (between the extremes within each dimension of inequality) as a proxy for absolute inequality.23 This was calculated by subtracting the coverage in one subgroup from another defined a priori across the five dimensions of inequality adopted from the WHO framework.17 23 Several equity analyses have shown that boys, urban dwellers, children of mothers with secondary or higher education and those in the richest quintile mostly have better access to health services compared with their peers in the other extreme.17 23 Thus, for child’s sex, we subtracted immunisation coverage for girls from that of boys; for place of residence, urban minus rural; for maternal education, senior secondary or higher education minus pre-primary or none; and region in a country, the region with highest coverage minus region with lowest coverage. We used this method to estimate the intra-country equity gap for BCG and DTP3 immunisation coverages. To estimate the intra-country equity gap in immunisation dropout, the first step was to calculate the immunisation dropout rate per subgroup in each of the dimensions; for example, we calculated the dropout in the male subgroup and female subgroup separately. Following this, we computed the difference in immunisation dropout between the subgroups similar to the scenario in BCG and DTP3 immunisation equity gaps calculation. Lastly, we displayed and compared the equity gaps for BCG, DTP3 and dropout across all five dimensions in the subregion using an Equiplot (a plot for equity analysis) according to the WHO Health Equity Assessment Toolkit Plus.23 To track the equity gap across the five dimensions, the GVAP recommended maximum gap of 20% points between those in the poorest and richest wealth quintile was adopted as the reference standard.8

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• Dima Health