Changing socioeconomic determinants of childhood vaccines: a global analysis over three decades

Background: Vaccine-preventable diseases cause important health, societal, and economic burdens worldwide. Although modern vaccines are highly efficacious, incomplete coverage results in preventable illness and death in both the developing and developed world. Identifying factors that may modulate coverage and understanding the vulnerability of immunisation programmes to dips in coverage levels are important for informing effective programmes and policies. Methods: We perform a large-scale correlative study to establish socioeconomic correlates of vaccine coverage. We analyse data from 178 countries and 259 socioeconomic and demographic factors across the six WHO-defined geographical regions, identifying those with the strongest correlation with coverage over 31 years (1980–2010) and over the most recent decade (2001–10) in each region. Diphtheria-tetanus-pertussis (DTP3) vaccination coverage was chosen as the focus as DTP3 is a common marker for immunisation coverage in the relevant literature. We fit Gaussian processes to vaccine coverage time-series and use predictive distributions over future coverage values to obtain a vaccine performance index which weighs the likelihood of high coverage against the chances of a large drop. Findings: Overall vaccine coverage has increased in all regions of the world over the past three decades, with marked variation in volatility and trends. Socioeconomic links to vaccine coverage are weakening worldwide. There are exceptions to this trend, including female education in the Middle East. Socioeconomic correlations with vaccine coverage are generally low in Europe, suggesting pockets of low coverage are more driven by intentional undervaccination or non-vaccination due to low vaccine confidence or alternative health beliefs rather than access issues. Interpretation: Understanding the drivers of vaccine acceptance to inform programmes and policies is challenging given regional variations. Review of historical trends and volatility in vaccination rates can aid policy makers' assessment of the strength and resilience of immunisation programmes. We see a marked improvement over the past decade across the globe providing evidence for higher, less volatile coverage; however, we identify key regions which are struggling to achieve high and steady coverage, notably in sub-Saharan Africa, parts of Asia, as well as some European countries where vaccine confidence has recently suffered. We believe that a vaccine performance index based on data that are routinely collected and available for most countries and patterns overtime can offer important support for immunisation programmes and policies which is complementary to survey metrics to investigate more volatile vaccine confidence issues. Funding: Bill & Melinda Gates Foundation, EPSRC, MRC