Global trends in vaccination coverage
Authors: Michiel van Boven, Alies van Lier
Journal: The Lancet Global Health (2016)

Universal vaccination programmes have greatly reduced the burden of infectious diseases in both developing and developed countries.1Cohen ML Changing patterns of infectious disease.Nature. 2000; 406: 762-767Crossref PubMed Scopus (647) Google Scholar, 2Ehreth J The global value of vaccination.Vaccine. 2003; 21: 596-600Crossref PubMed Scopus (233) Google Scholar, 3van Wijhe M McDonald SA de Melker HE Postma MJ Wallinga J Effect of vaccination programmes on mortality burden among children and young adults in the Netherlands during the 20th century: a historical analysis.Lancet Infect Dis. 2016; 16: 592-598Summary Full Text Full Text PDF PubMed Scopus (52) Google Scholar In the 1960s and 1970s, these reductions led to optimism that a victory in the battle against infectious diseases could be within reach. Unfortunately, even though the benefits of most childhood vaccinations are scientifically unquestioned, vaccination coverage rates are far from 100% in many countries, and show substantial variation. Early detection of trends and an improved understanding of underlying mechanisms are paramount to be able to improve vaccination policies. In The Lancet Global Health, Alexandre de Figueiredo and colleagues4de Figueiredo A Johnston IG Smith DMD Agarwal S Larson HJ Jones NS Correlations between forecasted trends in vaccination coverage and socioeconomic factors: a global time-series analysis over 30 years.Lancet Glob Health. 2016; (published online Aug 25.)http://dx.doi.org/10.1016/S2214-109X(16)30167-XGoogle Scholar take a step in this direction with their time-series analysis of trends in vaccine coverage and a suite of socioeconomic and demographic factors across 190 countries over 30 years. The main aim was to gauge where and when vaccination coverage might fall below levels that are safe for prevention of epidemic transmission, and to correlate such decreases with underlying socioeconomic and demographic factors. The investigators used WHO–UNICEF coverage estimates of three doses of diphtheria, tetanus, and pertussis (DTP3) vaccination and obtained data from Gapminder. By use of a statistical framework based on Gaussian process regression and a newly developed vaccine performance index, which forecasts that vaccination coverage will be at a safe level (90%) in the near future, the analyses yield some interesting results next to the basic fact that worldwide coverage has increased. For instance, gross domestic product (GDP) and government health spending correlate most strongly with vaccination coverage in Eastern Mediterranean countries between 1980 and 2010, whereas primary school completion correlates most strongly with vaccination coverage in Africa (more so than does GDP). The analyses also provide a list of countries with high to low vaccine performance indices, showing that many of the countries at the low end of the list are in sub-Saharan Africa, the Indian subcontinent, and southeast Asia. From a global public health perspective, the list provides an objective measure that can be used to prioritise countries or regions where efforts to increase vaccination coverage are expected to be most efficient. Notably, although vaccination coverage correlates well with GDP and schooling in many regions of the world, this is not the case any more in Europe and, to a lesser extent, North America. Here, no socioeconomic factors correlated with high coverage, and one argument is that once the basic necessities of life are available, other factors such as social attitudes to vaccination might become more important.5Milton H Mercier H Cognitive obstacles to pro-vaccination beliefs.Trends Cogn Sci. 2015; 19: 633-636Summary Full Text Full Text PDF PubMed Scopus (64) Google Scholar, 6Geelen E van Vliet H de Hoogh P Hortsman K Taming the fear of voice: dilemmas in maintaining a high vaccination rate in the Netherlands.Soc Sci Med. 2016; 153: 12-19Crossref PubMed Scopus (13) Google Scholar Because of the focus on socioeconomic factors, de Figueiredo and colleagues' findings cannot add much more than speculation to this argument, and it will be interesting to see the outcomes when the set of variables is extended to encompass social indicators that might shape vaccine hesitancy.7Larson HJ Jarret C Schulz WS et al.Measuring vaccine hesitancy: the development of a survey tool.Vaccine. 2015; 33: 4165-4175Crossref PubMed Scopus (398) Google Scholar With a focus on global immunisation patterns and the relation with socioeconomic factors, the investigators have painted a picture with broad brushes, one that cannot hope to unravel patterns that are important in specific regions or countries and for particular diseases. Examples are the difficulties encountered in the push towards eradication of polio in Afghanistan and Pakistan driven by war and extreme ideologies,8Toole MJ So close: remaining challenges to eradicating polio.BMC Med. 2016; 14: e43Crossref PubMed Scopus (22) Google Scholar the struggle to achieve elimination of measles in Europe given vaccine refusal in clustered religious and anthroposophical groups, and the perceived lack of safety of the human papillomavirus vaccine fuelled by adverse events after vaccination.9Larson H The world must accept that the HPV vaccine is safe.Nature. 2016; 528: 9Crossref Scopus (15) Google Scholar These examples show that a full understanding of local coverage patterns requires data and analyses at the local level. Technically, the vaccine performance index might have to be developed further. The index provides an aggregate measure that takes both vaccination coverage and changes in coverage into account. One could argue that in its current form the vaccine performance index punishes countries with systematically high but volatile vaccination coverage (eg, Norway) quite strongly. In fact, low vaccine performance indices in these countries might be due to reporting bias or small sample sizes (in cases when a national registry is not available). Indeed, in developing countries, precise figures for vaccination coverage are often not available, and estimation of vaccination coverage is not always straightforward.10Lessler J Metcalf CJ Grais RF Luquero FJ Cummings DA Grenfell BT Measuring the performance of vaccination programs using cross-sectional surveys: a likelihood framework and retrospective analysis.PLoS Med. 2011; 8: e1001110Crossref PubMed Scopus (43) Google Scholar, 11Pramanik S Muthusamy N Gera R Laxminarayan R Vaccination coverage in India: a small area estimation approach.Vaccine. 2015; 33: 1731-1738Crossref PubMed Scopus (12) Google Scholar Future developments will probably have to incorporate the uncertainty in vaccination coverage estimates to prevent artificial increases in the precision of the correlations. Overall, de Figueiredo and colleagues have provided a laudable analysis of the link between vaccination coverage rates and demographic and socioeconomic factors at the global scale. In addition to providing an overview of trends and potential explanations, an important merit of the study is that it forces us to think about the factors that determine vaccination coverage now and in the future. We declare no competing interests. We thank Hans van Vliet, Hester de Melker, Liesbeth Mollema, and Marianne van der Sande for helpful discussion. Forecasted trends in vaccination coverage and correlations with socioeconomic factors: a global time-series analysis over 30 yearsOur vaccine performance index highlighted countries at risk of failing to achieve the GVAP target of 90% coverage by 2015, and could aid policy makers' assessments of the strength and resilience of immunisation programmes. Weakening correlations with socioeconomic factors show a need to tackle vaccine confidence, whereas strengthening correlations point to clear factors to address. Full-Text PDF Open Access