Abstract
BACKGROUND: We aimed to evaluate the impact of a Private Provider Engagement (PPE) model that integrated neighborhood private health providers into the immunization system to improve vaccine uptake and reduce coverage disparities among marginalized communities in Karachi, Pakistan, where health inequities and the risk of vaccine-preventable diseases remain high. METHODS: Routine immunization service corners were established at nine private clinics in urban settlements of eight high-risk union councils (HRUCs) in Karachi. A quasi-experimental before-and-after study design was used with a baseline survey conducted in May-July 2022 and an end-line survey in April-June 2024. Households were selected using a multistage cluster sampling approach, and data were collected from parents or primary caregivers of children aged 4-11 months residing in the catchment areas for >3 months, using an adapted WHO immunization coverage questionnaire. The primary outcome was child immunization status for BCG, Polio, Pentavalent (DTP-3), Rotavirus, PCV, TCV, and MR vaccines, categorized as fully vaccinated, partially vaccinated, or unvaccinated, and verified through vaccination cards or caregiver recall. Multinomial and binary logistic regression were used to investigate factors associated with immunization coverage. RESULTS: A total of 2167 children were surveyed (1141 children at baseline; 1026 children at end-line). The proportion of fully immunized children more than doubled across sexes, with significantly higher adjusted odds at endline (aOR: 6.34, 95%CI: 2.45-16.21). Age-appropriate uptake of all antigens improved, with over fourfold odds for receiving the Penta-3 vaccine (aOR 4.55, 95%CI: 3.55-5.82) and more than threefold odds for receiving the MR-1 Vaccine (aOR 3.67, 95%CI: 2.37-5.67). Parental education strongly predicted immunization, with the highest odds among children of fathers with secondary or higher education or skilled labor. Fully immunized Pashto-speaking children increased at endline but had the lowest odds compared to Urdu-speaking children. CONCLUSION: The PPE model increased vaccination coverage and reduced disparities in Karachi's urban settlements, demonstrating potential for scale-up to strengthen routine immunization and reduce the number of zero-dose children.