Exploring socio-economic inequalities in measles immunisation in Lao People's Democratic Republic, Thailand, and Viet Nam

BACKGROUND: Recent surges in measles infections in Southeast Asia highlight the importance of equitable measles immunisation. However, inequalities in access to measles vaccines persist in the region, influenced by various social determinants. This study aims to explore wealth-related inequalities in receiving the first dose of measles vaccine (MCV1) among children aged 9-23 months. METHODS: We utilised the most recent Multiple Indicators Cluster Survey (MICS) of Lao PDR (2023), Thailand (2022), and Viet Nam (2020-21). We used multivariable regression models to identify predictors of receiving MCV1. We analysed wealth-related inequalities in receiving MCV1 using concentration index (CIX) and concentration curve (CCX). RESULTS: Our study included a total of 3791 samples of children aged 9-23 months, with sample size per country: Lao PDR = 1393; Thailand = 1646, and Viet Nam = 752, of which 71.21%, 85.54%, and 74.34% of children were vaccinated with MCV1, respectively. We found that child's age is associated with receiving first dose of measles immunisation in all countries, while parity was correlated with MCV1 inoculation in Lao PDR and Thailand. Additionally, maternal education and wealth quintiles were predictors of receiving MCV1 in Thailand and Lao PDR, respectively. Our analyses of CIX and CCX showed that wealth-related inequalities in the receipt of MCV1 was significant in Lao PDR (CIX: 0.052, 95% CI: 0.031-0.074, p < 0.0001); while in Thailand (CIX: 0.001, 95% CI: -0.20-0.022, p < 0.952) and Viet Nam (CIX: 0.018, 95% CI: -0.016-0.052, p < 0.306), the measured wealth inequalities in receiving MCV1 appear to be insignificant. CONCLUSION: Wealth inequalities significantly influence measles immunisation coverage in countries with relatively suboptimal primary healthcare system. Strengthening of universal healthcare coverage, which plays a critical role in reducing health disparities between rich and poor, is essential to drive equitable access to immunisation and mitigate the threats of future outbreaks.