**5. Conclusions**

This study establishes an association between being a zero-dose child and homebased births, being the younger child, being born to immigrant fathers, and minority non-Christian mothers. Therefore, the study highlights the need to develop context-specific approaches to vaccinating children in hard-to-reach communities to close health equity gaps. This can be achieved by paying more attention to minority groups, immigrants, and younger children, including newborns, who are often missed during vaccination campaigns. The study findings also reemphasize the value of SIA in such a missed community.

#### *5.1. Limitations*

A major flaw in this study is the possibility of non-differential misclassification of the vaccination status of children since more than 90% of children did not have birth certificates, and their ages were estimated based on their parents' recall. Although this may have affected the proportion of incomplete and complete vaccination cases, it did not affect the multivariable logistic regression findings because the outcome variable was solely based on whether the child had ever received any vaccine antigen on the Cameroon EPI calendar (zero-dose vaccination status). Also, we minimized bias stemming from the caregiver's recall by corroborating the children's vaccination status with a checklist of timing of SIA and national vaccination campaigns in the past five years.

The certainty of the evidence is limited by the small sample size of specific populations, such as non-Christian mothers and fathers, and the number of health facility-based births. Apart from the limited statistical power of this study, the cross-sectional study design conducted using secondary data posed a challenge of generalizability. However, the findings are aligned with many similar studies in other countries.

Convenience sampling was employed which, may have compromised the generalizability of this study. However, the sampling approach took into consideration the most populous islets in MHD with high zero-dose proportion. The population dynamics and social activities of these communities make availability a major issue—this is the reason why convenience sampling was a great fit so as not to lose valuable data.

#### *5.2. Recommendation*

A qualitative study to establish in-depth reasons for zero-dose and under-vaccinated children will further close the knowledge gap on missed communities in Cameroon.

**Author Contributions:** Conceptualization, S.C.N.; methodology, S.C.N.; data curation, S.C.N.; formal analysis; writing—original draft preparation, S.C.N.; writing—review and editing, Y.S., V.N.A., C.M.M., N.J.M., A.A.N., S.T.N., B.N., N.N.E. and C.S.Z.; supervision, Y.S., S.R. and C.S.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. The primary data collection was funded by Gavi through CHAI. These institutions had no role in the preparation and submission of this manuscript.

**Institutional Review Board Statement:** This study was conducted in compliance with the Helsinki Declaration and all applicable national laws and institutional rules and has been approved by the author's institutional review board. Ethical approval was granted by the Cameroon National Ethics Committee for Human Health Research with the reference 2019/07/1174/CE/CNERSH/SP on the 12 of July 2019.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data used for this research are available from the corresponding author upon reasonable request.

**Acknowledgments:** Our gratitude to Clinton Health Access Initiative, Cameroon, for granting us access to this data and to Gavi the vaccine alliance, for providing the funds for the primary survey. Also, we would like to acknowledge the staff and IMPH research committee at the Hebrew University and Hadassah Braun School of Public Health and Community Medicine, Jerusalem, Israel.

**Conflicts of Interest:** The authors declare no conflict of interest.
