A standardized approach for measuring multivariate equity in vaccination coverage, cost-of-illness, and health outcomes: Evidence from the Vaccine Economics Research for Sustainability & Equity (VERSE) project

Inequality in Childhood Immunization Coverage: A Scoping Review of Data Sources, Analyses, and Reporting Methods

Immunization through vaccines among children has contributed to improved childhood survival and health outcomes globally. However, vaccine coverage among children is unevenly distributed across settings and populations. The measurement of inequalities is essential for understanding gaps in vaccine coverage affecting certain sub-populations and monitoring progress towards achieving equity. Our study aimed to characterize the methods of reporting inequalities in childhood vaccine coverage, inclusive of the settings, data source types, analytical methods, and reporting modalities used to quantify and communicate inequality. We conducted a scoping review of publications in academic journals which included analyses of inequalities in vaccination among children. Literature searches were conducted in PubMed and Web of Science and included relevant articles published between 8 December 2013 and 7 December 2023. Overall, 242 publications were identified, including 204 assessing inequalities in a single country and 38 assessing inequalities across more than one country. We observed that analyses on inequalities in childhood vaccine coverage rely heavily on Demographic Health Survey (DHS) or Multiple Indicator Cluster Surveys (MICS) data (39.3%), and papers leveraging these data had increased in the last decade. Additionally, about half of the single-country studies were conducted in low- and middle-income countries. We found that few studies analyzed and reported inequalities using summary measures of health inequality and largely used the odds ratio resulting from logistic regression models for analyses. The most analyzed dimensions of inequality were economic status and maternal education, and the most common vaccine outcome indicator was full vaccination with the recommended vaccine schedule. However, the definition and construction of both dimensions of inequality and vaccine coverage measures varied across studies, and a variety of approaches were used to study inequalities in vaccine coverage across contexts. Overall, harmonizing methods for selecting and categorizing dimensions of inequalities as well as methods for analyzing and reporting inequalities can improve our ability to assess the magnitude and patterns of inequality in vaccine coverage and compare those inequalities across settings and time.

Equity in vaccine coverage in Uganda from 2000 to 2016: revealing the multifaceted nature of inequity

BACKGROUND

This study analyses vaccine coverage and equity among children under five years of age in Uganda based on the 2016 Uganda Demographic and Health Survey (UDHS) dataset. Understanding equity in vaccine access and the determinants is crucial for the redress of emerging as well as persistent inequities.

METHODS

Applied to the UDHS for 2000, 2006, 2011, and 2016, the Vaccine Economics Research for Sustainability and Equity (VERSE) Equity Toolkit provides a multivariate assessment of immunization coverage and equity by (1) ranking the sample population with a composite direct unfairness index, (2) generating quantitative measure of efficiency (coverage) and equity, and (3) decomposing inequity into its contributing factors. The direct unfairness ranking variable is the predicted vaccination coverage from a logistic model based upon fair and unfair sources of variation in vaccination coverage. Our fair source of variation is defined as the child's age - children too young to receive routine immunization are not expected to be vaccinated. Unfair sources of variation are the child's region of residence, and whether they live in an urban or rural area, the mother's education level, the household's socioeconomic status, the child's sex, and their insurance coverage status. For each unfair source of variation, we identify a "more privileged" situation.

RESULTS

The coverage and equity of the Diphtheria-Pertussis-Tetanus vaccine, 3rd dose (DPT3) and the Measles-Containing Vaccine, 1st dose (MCV1) - two vaccines indicative of the health system's performance - improved significantly since 2000, from 49.7% to 76.8% and 67.8% to 82.7%, respectively, and there are fewer zero-dose children: from 8.4% to 2.2%. Improvements in retaining children in the program so that they complete the immunization schedule are more modest (from 38.1% to 40.8%). Progress in coverage was pro-poor, with concentration indices (wealth only) moving from 0.127 (DPT3) and 0.123 (MCV1) in 2000 to -0.042 and -0.029 in 2016. Gains in overall equity (composite) were more modest, albeit significant for most vaccines except for MCV1: concentration indices of 0.150 (DPT3) and 0.087 (MCV1) in 2000 and 0.054 and 0.055 in 2016. The influence of the region and settings (urban/rural) of residence significantly decreased since 2000.

CONCLUSION

The past two decades have seen significant improvements in vaccine coverage and equity, thanks to the efforts to strengthen routine immunization and ongoing supplemental immunization activities such as the Family Health Days. While maintaining the regular provision of vaccines to all regions, efforts should be made to alleviate the impact of low maternal education and literacy on vaccination uptake.

Multivariate Assessment of Vaccine Equity in Cambodia: A Longitudinal VERSE Tool Case Study Using Demographic and Health Survey 2004, 2010, and 2014

Cambodia has exhibited great progress in achieving high coverage in nationally recommended immunizations. As vaccination program managers plan interventions to reach last-mile children, it is important to consider issues of equity immunization priority setting. In this analysis, we apply the VERSE Equity Tool to Cambodia’s Demographic and Health Survey for the years 2004, 2010, and 2014 to evaluate multivariate equity in vaccine coverage for 11 vaccination statuses, emphasizing the results of the 2014 survey for MCV1, DTP3, fully immunized for age (FULL), and zero dose (ZERO). The largest drivers of vaccination inequity are socioeconomic status and the educational attainment of the child’s mother. MCV1, DTP3, and FULL exhibit increasing levels of both coverage and equity with increasing survey years. The national composite Wagstaff concentration index values from the 2014 survey for DTP3, MCV1, ZERO, and FULL are 0.089, 0.068, 0.573, and 0.087, respectively. The difference in vaccination status coverage between the most and least advantaged quintiles of Cambodia’s population, using multivariate ranking criteria, is 23.5% for DTP3, 19.5% for MCV1, 9.1% for ZERO, and 30.3% for FULL. By utilizing these VERSE Equity Tool outputs, immunization program leaders in Cambodia can identify subnational regions in need of targeted interventions.

Comparing Multivariate with Wealth-Based Inequity in Vaccination Coverage in 56 Countries: Toward a Better Measure of Equity in Vaccination Coverage

INTRODUCTION

Following a call from the World Health Organization in 2017 for a methodology to monitor immunization coverage equity in line with the 2030 Agenda for Sustainable Development, this study applies the Vaccine Economics Research for Sustainability and Equity (VERSE) vaccination equity toolkit to measure national-level inequity in immunization coverage using a multidimensional ranking procedure and compares this with traditional wealth-quintile based ranking methods for assessing inequity. The analysis covers 56 countries with a most recent Demographic & Health Survey (DHS) between 2010 and 2022. The vaccines examined include Bacillus Calmette-Guerin (BCG), Diphtheria-Tetanus-Pertussis-containing vaccine doses 1 through 3 (DTP1-3), polio vaccine doses 1-3 (Polio1-3), the measles-containing vaccine first dose (MCV1), and an indicator for being fully immunized for age with each of these vaccines.

MATERIALS & METHODS

The VERSE equity toolkit is applied to 56 DHS surveys to rank individuals by multiple disadvantages in vaccination coverage, incorporating place of residence (urban/rural), geographic region, maternal education, household wealth, sex of the child, and health insurance coverage. This rank is used to estimate a concentration index and absolute equity coverage gap (AEG) between the top and bottom quintiles, ranked by multiple disadvantages. The multivariate concentration index and AEG are then compared with traditional concentration index and AEG measures, which use household wealth as the sole criterion for ranking individuals and determining quintiles.

RESULTS

We find significant differences between the two sets of measures in almost all settings. For fully-immunized for age status, the inequities captured using the multivariate metric are between 32% and 324% larger than what would be captured examining inequities using traditional metrics. This results in a missed coverage gap of between 1.1 and 46.4 percentage points between the most and least advantaged.

CONCLUSIONS

The VERSE equity toolkit demonstrated that wealth-based inequity measures systematically underestimate the gap between the most and least advantaged in fully-immunized for age coverage, correlated with maternal education, geography, and sex by 1.1-46.4 percentage points, globally. Closing the coverage gap between the bottom and top wealth quintiles is unlikely to eliminate persistent socio-demographic inequities in either coverage or access to vaccines. The results suggest that pro-poor interventions and programs utilizing needs-based targeting, which reflects poverty only, should expand their targeting criteria to include other dimensions to reduce systemic inequalities, holistically. Additionally, a multivariate metric should be considered when setting targets and measuring progress toward reducing inequities in healthcare coverage.

Coverage and Equity of Childhood Vaccines in China

IMPORTANCE

Measuring vaccination coverage rates and equity is crucial for informing immunization policies in China.

OBJECTIVES

To estimate coverage rates and multidimensional equity for childhood vaccination in China.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study was conducted via a survey in 10 Chinese provinces between August 5 and October 16, 2019, among children ages 6 months to 5 years and their primary caregivers. Children's vaccination records and their primary caregivers' demographics and socioeconomic status were collected. Data were analyzed from November 2019 to March 2022.

MAIN OUTCOMES AND MEASURES

Vaccine coverage rates were measured as a percentage of National Immunization Program (NIP) and non-NIP vaccines administered before the day on which the child was surveyed. A multidimensional equity model applied a standardized approach to ranking individuals from least to most unfairly disadvantaged by estimating differences between observed vaccination status and estimated vaccination status as function of fair and unfair variation. Fair sources of variation in coverage included whether the child was of age to receive the vaccine, and unfair sources of variation included sex of the child and sociodemographic characteristics of caregivers. Absolute equity gaps (AEGs), concentration index values, and decompositions of factors associated with vaccine equity were estimated in the model.

RESULTS

Vaccine records and sociodemographic information of 5294 children (2976 [52.8%] boys and 2498 [47.2%] girls; age range, 6-59 months; 1547 children aged 12-23 months) and their primary caregivers were collected from 10 provinces. Fully immunized coverage under the NIP was 83.1% (95% CI, 82.0%-84.1%) at the national level and more than 80% in 7 provinces (province coverage ranged from 77.8% [95% CI, 74.3% to 81.3%] in Jiangxi to 88.4% [95% CI, 85.7%-91.1%] in Beijing). For most non-NIP vaccines, however, coverage rates were less than 50%, ranging from 1.8% (95% CI, 1.3%-2.2%) for the third dose of rotavirus vaccine to 67.1% (65.4% to 68.8%) for the first dose of the varicella vaccine. The first dose of Haemophilus influenzae type b vaccine had the largest AEG, at 0.603 (95% CI, 0.570-0.636), and rotavirus vaccine dose 3 had the largest concentration index value, at 0.769 (95% CI, 0.709-0.829). The largest share of non-NIP vaccine inequity was contributed by monthly family income per capita, followed by education level, place of residence, and province for caregivers. For example, the proportion of explained inequity for pneumococcal conjugate vaccine dose 3 was 40.94% (95% CI, 39.49%-42.39%), 22.67% (95% CI, 21.43%-23.9%), 27.15% (95% CI, 25.84%-28.46%), and 0.68% (95% CI, 0.44%-0.92%) for these factors, respectively.

CONCLUSIONS AND RELEVANCE

This cross-sectional study found that NIP vaccination coverage in China was high but there was inequity for non-NIP vaccines. These findings suggest that improvements in equitable coverage of non-NIP vaccination may be urgently needed to meet national immunization goals.