Introduction: Coverage of health interventions usually shows social gradients with higher levels among wealthy than among poor individuals. Owing to the upsurge of vaccine hesitancy in highincome countries, the authors hypothesized that the social gradient may also be changing over time in the low-and middle-income countries and set out to test this hypothesis.Methods: In January 2020, surveys conducted from 2010 to 2018 in 86 low-and middle-income countries were analyzed to assess full immunization coverage in children aged 12−23 months. The authors calculated full immunization coverage point estimates and 95% CIs for each country and wealth quintile. To explore wealth-related inequalities, the authors estimated the slope index of inequality and calculated the Pearson correlation coefficient between these values and per capita gross domestic product. Time trends were analyzed in 10 countries with recent evidence of hesitancy.Results: Pro-poor patterns were defined as significant slope index of inequality values with higher coverage among poor children, and pro-rich patterns were defined as the reverse pattern. A total of 11 countries showed pro-poor patterns in the most recent survey, accounting for 20% of upper middle− and 7% of low-income countries. The correlation between the slope index of inequality and log per capita gross domestic product was À0.38 (p<0.001). Among the 10 countries with recent evidence of hesitancy, 5 showed full immunization coverage declines over time in the wealthiest quintiles, and 4 switched from pro-rich to pro-poor patterns throughout the years.Conclusions: Lower full immunization coverage was found among the wealthy than among the poor in 10 countries, especially in the upper middle−income group, consistent with the emergence of vaccine hesitancy.
