Abstract
Background: Large urban centers in low- and middle-income countries (LMICs) often have persistent pockets of under-immunized children, despite higher overall vaccination coverage than rural areas. Lahore, a megacity in Pakistan, had the lowest rate of fully immunized children in Punjab province as of 2022 (70%), partly due to challenges in its urban slums. In 2023, an innovative intervention was implemented, utilizing Pakistan's extensive polio eradication workforce to identify and reach children who were missing routine vaccinations. Objective: The objective was to assess changes in routine immunization coverage during a pre-post evaluation period in which polio campaign workers were engaged to support routine immunization among under-immunized urban populations in Lahore. Methods: A special outreach strategy engaged polio vaccination teams to conduct door-to-door visits of children aged 12-23 months, recording each child's routine immunization status. These data were integrated into the electronic health system and provided to Expanded Programme on Immunization (EPI) staff for targeted follow-up. Two cross-sectional household surveys of caregivers of children aged 12-23 months were conducted: a 2022 baseline survey and a 2023 follow-up survey conducted six months after implementation. Both surveys used two-stage cluster sampling and WHO-standard immunization coverage methods, with vaccination status verified using cards or caregiver recall. Results: A total of 773 children were surveyed at baseline and 780 at endline. Full immunization coverage increased from 69.8% (CI: 64.13-74.98) to 85.1% (CI: 81.01-88.51). Partial immunization declined from 26.9% (CI: 22.37-31.92) to 14.5% (CI: 11.27-18.50), and the proportion of children not vaccinated at all dropped from 3.3% (CI: 1.92-5.60) to 0.3% (CI: 0.11-0.98). Penta-3 coverage improved from 83.2% (CI: 78.65-87.04) to 94.1% (CI: 91.15-96.07), and Measles 1 from 76.9% (CI: 71.80-81.40) % to 92.1% (CI: 88.71-94.56). Immunization card retention increased from 69.9% (CI: 64.15-75.16) to 84% (CI:81.19-86.94). Improvements were observed across all socio-demographic groups, with a higher impact in peri-urban clusters and low socio-economic groups, and all remained statistically significant. Conclusions: Our findings showed improvements in routine immunization coverage in urban Lahore between 2022 and 2023. This period coincided with district-wide implementation of a polio worker outreach strategy as well as the broader post-COVID-19 recovery of immunization services. This study lacked a control group; therefore, the findings indicate a temporal association occurring during the post COVID-19 recovery period, rather than definitive evidence of causal impact. Nonetheless, integrating the workforce of the polio program into routine immunization could be a promising programmatic strategy to close immunization gaps in urban areas.