**2. Methods**

We conducted a systematic search of the published literature to identify relevant information and data on backsliding of immunization coverage in urban settings during the COVID-19 pandemic, the predictors and challenges of routine immunization and pro-equity strategies relevant to urban and peri-urban settings. Priority was given to the 20 high-burden zero-dose countries, per the 2021 WHO and UNICEF Estimates of National Immunization Coverage (WUENIC). This study has the following research questions prioritized for the review:


The literature reviewed were from 2 databases, namely, PubMed and Web of Science, due to their broad coverage of health sciences, and inclusive of published literature in the 20 high-burden zero-dose countries for the period between March 2020 and January 2023, to cover the period of COVID-19 pandemic. Search terms used were "immunization coverage" and "urban" and were limited to twenty countries and the period of March 2020 to January 2023. The paper types include ecological studies, cross sectional, interventional, and pre- and post-studies. The full search strategy is available in Appendix A.2.

A total of 608 articles were identified from both databases (PubMed = 321 and Web of Science = 287), which were imported into Rayyan (rayyan.ai). Screening of records detected and removed 227 duplicates. The title and abstract screening of 318 articles based on our inclusion criteria was conducted by 2 authors, ID and RB. The blind decisions by both authors for inclusion were 90% aligned. The reviewers reviewed the misaligned articles and agreed on the final decision according to the criteria in Table 1. Thirty-seven articles were identified for inclusion after the title and abstract review. The remaining articles were screened and excluded if the papers fell outside the designated time period, did not contain references to urban populations or areas, and did not contain references to COVID-19. A flow chart for the literature review is included in Figure 1. A final 15 articles were included in the review, analyzed, and presented in this study.

**Figure 1.** PRISMA Flow chart for the review of papers.




**Table 1.** *Cont.*
