 Over the last two decades, there has been an improvement in the quality of global immunization coverage data. However, this improvement has not been uniform across regions or countries. This study found that the probability of data quality flags decreased by 5.1% per year globally, with the steepest declines occurring in Africa, minus 9.6%, minus 13.0%, to minus 5.8%, P less than 0.001, followed by Europe, minus 5.4%, minus 9.2 to minus 1.6, P equals 0.0055, and the Americas, minus 4.9%, minus 9.2 to minus 0.6, P equals 0.026. Additionally, most country groups showed a statistically significant decline, and none had a statistically significant increase. These findings suggest that more work needs to be done to ensure that all countries are reporting accurate and reliable immunization coverage data.