Local trends in immunisation coverage across Africa
Authors: Alexandre de Figueiredo, Fredrick Were
Journal: The Lancet (2019)

Immunisation coverage across Africa has greatly increased over the past few decades, with corresponding reductions in disease mortality and morbidity.1Arevshatian L Clements C Lwanga S et al.An evaluation of infant immunization in Africa: is a transformation in progress?.Bull World Health Organ. 2007; 85: 449-457Google Scholar Future increases in coverage are anticipated to return large health benefits,2Ozawa S Clark S Portnoy A et al.Estimated economic impact of vaccinations in 73 low- and middle-income countries, 2001–2020.Bull World Health Organ. 2017; 95: 629-638Google Scholar but coverage rates in many countries across the continent are far from national targets, with many rates stagnating or falling.3de Figueiredo A Johnston IG Smith DM Agarwal S Larson HJ Jones NS Forecasted trends in vaccination coverage and correlations with socioeconomic factors: a global time-series analysis over 30 years.Lancet Glob Health. 2016; 4: e726-e735Google Scholar, 4WHOData, statistics and graphics: official country reported and WHO-UNICEF coverage estimates.https://www.who.int/immunization/monitoring_surveillance/data/en/Date: 2019Date accessed: February 28, 2019Google Scholar This incomplete coverage across Africa is still a major contributor to child mortality and morbidity.5Liu L Oza S Hogan D et al.Global, regional, and national causes of under-5 mortality in 2000–15: an updated systematic analysis with implications for the Sustainable Development Goals.Lancet. 2016; 388: 3027-3035Google Scholar Although national and first-level administrative estimates of routine coverage are assessed annually,4WHOData, statistics and graphics: official country reported and WHO-UNICEF coverage estimates.https://www.who.int/immunization/monitoring_surveillance/data/en/Date: 2019Date accessed: February 28, 2019Google Scholar they conceal heterogeneities in coverage at fine spatial scales, precluding a comprehensive quantitative assessment of local barriers to vaccination and their potential effect on disease burdens. From an African public health perspective, more local assessments of coverage can help to identify areas with vaccine delivery system weakness and help to support more precisely targeted interventions—for example, by building upon existing research into the link between travel networks and coverage.6Metcalf CJ Tatem A Bjornstad ON et al.Transport networks and inequities in vaccination: remoteness shapes measles vaccine coverage and prospects for elimination across Africa.Epidemiol Infect. 2015; 143: 1457-1466Google Scholar In The Lancet, Jonathan Mosser and colleagues7Mosser JF Gagne-Maynard W Rao PC et al.Mapping diphtheria-pertussis-tetanus vaccine coverage in Africa, 2000–2016: a spatial and temporal modelling study.Lancet. 2019; (published online April 5.)http://dx.doi.org/10.1016/S0140-6736(19)30226-0Google Scholar report estimates of diphtheria-pertussis-tetanus (DPT) vaccine coverage across the African continent at highly localised scales. With use of large-scale public health data from 49 African countries between 2000 and 2016, the authors identified local heterogeneities in DPT coverage and dropout between the first (DPT1) and third (DPT3) doses of the programme. The authors highlighted regions with persistently low coverage and high vaccine dropout rates and assessed coverage with a focus on the 80% coverage target for administrative-level units set by the Global Vaccine Action Plan (GVAP). Although geospatial models have been used previously for subnational coverage estimation in Africa,8Takahashi S Metcalf CJE Ferrari MJ Tatem AJ Lessler J The geography of measles vaccination in the African Great Lakes region.Nature Commun. 2017; 8: 15585Google Scholar this analysis represents a major leap in both the breadth (a continental analysis) and the volume of data used. Mosser and colleagues used almost 1 million immunisation records from 49 African countries by use of 183 household surveys hosted at the Global Health Data Exchange. Local coverage estimates were obtained with a Bayesian geostatistical model allowing coverage to be inferred at spatiotemporal points across Africa. Through this inference of yearly, spatially resolved estimates, Mosser and colleagues revealed novel insights in the geographical distribution of DPT coverage across Africa. For instance, they found that although DPT3 coverage increased in 72·3% (95% uncertainty interval [UI] 64·6–80·3) of second-level administrative units across the continent between 2000 and 2016, DPT3 coverage also decreased in 27·7% (19·7–35·4) of these units during the same time, pointing to stark spatiotemporal DPT coverage inequalities. Indeed, eight African countries were found to contain at least one second-level administrative unit with DPT3 coverage that was less than half the national average, including Nigeria and Ethiopia. Additionally, Ethiopia has the largest subnational coverage variation observed across the continent (from 93·1% [95% UI 89·1–95·9] in Addis Ababa to 9·7% [5·7–15·1] in Fantena Rasu). Despite the growth in DPT coverage across Africa, Mosser and colleagues found that only two countries met GVAP's subnational immunisation target9Global Vaccine Action PlanMonitoring, evaluation & accountability: secretariat annual report 2018. World Health Organization, Geneva2018Google Scholar of 80% coverage in all second-level administrative units in 2016: Morocco and Rwanda. Although this number has improved from zero in 2000, it still represents suboptimal progress given that emphasis is now shifting from reaching every district to reaching every child.10WHORegional strategic plan for immunization: 2014–2020. World Health Organization, Geneva2015Google Scholar From both a modelling and a policy perspective, the spatial coverage estimates developed by Mosser and colleagues might need to be developed further in high-density urban settings. The minimal spatial scale used by the authors (5 km × 5 km) is likely to mask urban variations in coverage, particularly where access to vaccination is strongly linked to income inequalities (such as informal vs formal residential areas). Although this is potentially a problem with the GVAP targets themselves (which focus on administrative levels rather than local population densities), a geostatistical approach based on local populations rather than a fixed spatial scale might increase the ability to identify at-risk groups. Mosser and colleagues have provided a commendable analysis of vaccination coverage across Africa at fine spatial scales, providing valuable summaries of subnational and transnational trends assessed with a focus on coverage targets. We declare no competing interests. Mapping diphtheria-pertussis-tetanus vaccine coverage in Africa, 2000–2016: a spatial and temporal modelling studyDespite substantial progress in Africa, marked national and subnational inequalities in DPT coverage persist throughout the continent. These results can help identify areas of low coverage and vaccine delivery system vulnerabilities and can ultimately support more precise targeting of resources to improve vaccine coverage and health outcomes for African children. Full-Text PDF Open Access