Leveraging Data from a Provincial Electronic Immunization Registry to Analyze Immunization Coverage, Timeliness, and Defaulters Among 8.8 Million Children from the 2018 to 2023 Birth Cohorts in Sindh Province, Pakistan

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Background/Objectives: Full immunization coverage in Pakistan remains suboptimal at 66%. An in-depth assessment is needed to understand the long-term trends in immunization and identify the extent of defaulters and associated risk factors of them being left uncovered by the immunization system. Methods: We conducted a 5-year analysis using the Government’s Provincial Electronic Immunization Registry data for the 2018–2023 birth cohorts in Sindh province. We analyzed 8,792,392 child-level immunization records from 1 January 2018 to 31 May 2024 to examine trends in immunization coverage, timeliness, defaulter rates, and associated risk factors; Results: Our findings indicate gradual improvements in immunization coverage, with full immunization rates increasing by 23.2% (from 47.5% to 70.7%) from 2018 to 2022. While timeliness declined from 2018 to 2021, it recovered in 2022 and 2023. Over the 5-year study period, >90% of children defaulted on vaccinations, with 34.8% fully covered and 9.1% uncovered. Children from urban areas (OR = 1.54; 95% CI = 1.52, 1.56; p-value < 0.001) and those enrolled through fixed immunization sites (OR = 2.11; 95% CI = 2.08, 2.15; p-value < 0.001) and mobile immunization vans (OR = 1.13; 95% CI = 1.13, 1.77; p-value = 0.003) were at higher risk of being uncovered defaulters. Conclusions: This study demonstrates improvements in immunization coverage in Sindh while highlighting the challenge of low timeliness and high default rates. Our findings provide insights to strengthen immunization access and timeliness, particularly in high-default areas, and can guide policies in similar low-income settings for more equitable and comprehensive immunization coverage.