Determinants of Parental Adherence to Childhood Immunization Among Children Under Five in Marginalized Asian Populations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Detailed Article Report 

Article Title: Determinants of Parental Adherence to Childhood Immunization in Under-Five Maginalized Populations in Asia: A Systematic  Review. 

Authors: Nitima Nulong, Nirachon Chutipattana, Lan T.K. Nguyen, An Dai Tran, Uyen T.T. Nguyen and Cua Ngoc Le 

 

Brief summary  

This paper is a review of the factors influencing parental adherence to childhood vaccination in marginalized populations in Asia. It analyzes 21 studies between 2015 and 2025, identifying five key domains: 1) socioeconomic and access factors, 2) trust, cultural beliefs, and social norms, 3) migration and mobility, 4) household and caregiver dynamics, and 5) health system capacity. It indicates in a descriptive way the possible biases of the included studies. 

 

General concept comments 
 

Conceptual framework 

I recommend clarifying in the introduction some concepts that are mentioned later, which may be unknown or confusing to some readers, such as: Left-behind children, Rohingya refugee, makeshift camps, slums and haor communities. 

Type of review 

In the 2.1. Study selection section (methodology), it is indicated that "a narrative literature review" was carried out, also in line 162 "Given the narrative design of this review...". However, in the title, the summary or point 2.3. Search strategy is called "systematic review". Although it uses tools typical of a systematic review (such as PRISMA and inclusion/exclusion criteria), the analysis approach and presentation of results (mainly as a Thematic synthesis) is narrative. On the other hand, no formal quantitative evaluation has been carried out nor statistical aggregation criteria have been applied (typical of systematic reviews and/or meta-analyses), and diverse studies are included in terms of types and sources seeking breadth rather than statistical precision (in addition, this diversity makes a meta-analysis impossible, as the authors themselves acknowledge in line 146). Therefore, according to the latest trends, it is a narrative review with a systematic approach, also known as an integrative review; It would not be a "systematic review" as such. I recommend that the authors consider this change. 

Search process 

On the other hand, regarding the search process, it is stated that different sources were used to extract information: "bibliographic databases (PubMed, Scopus, Google Scholar) and organizational reports (WHO, UNICEF, Gavi, and DHS)". However, in the flowchart only PubMed, Scopus and Google Scholar appear as a source of eligible studies. What use did WHO, UNICEF, Gavi, and DHS have? If they were not source resources for the publications selected in this review, they should be deleted. 

Data consistency 

The flowchart indicates that Google Scholar initially yielded 407 records. However, in table A1 of the appendix, "First 200 results screened" is indicated. This incongruity must be reviewed. 

 

Specific comments  

In the summary, I recommend numbering (1)...; 2)…) the five domains that influenced adherence.  

In 2.2. Eligible criteria, line 90 presents the phrase "We excluded studies on adult immunization, non-Asian contexts, non-marginalized populations". Exclusion criteria are not the opposite of inclusion criteria. Therefore, this part of the sentence can be ignored. 

Line 106 of 2.3. Search strategy: the sources "bibliographic databases (PubMed, Scopus, Google Scholar) and organizational reports (WHO, UNICEF, Gavi, and DHS)" were already named in point 2.1., so they can be omitted here so as not to repeat information. 

Appendix B: It may be a file download error, but aren't the determinants "Trust & cultural beliefs"/"Health system & program" and "Household dynamics"/"Migration & mobility" also connected to each other? 

 

 

• The manuscript is clear, relevant for the field, and presented in a well-structured manner. The cited references are mostly recent publications (within the last 5 years) and do not include an excessive number of self-citations. The conclusions are consistent with the evidence and arguments presented.  

Comments for author File: Comments.pdf

Author Response

Comment 1: I recommend clarifying in the introduction some concepts that are mentioned later, which may be unknown or confusing to some readers, such as: Left-behind children, Rohingya refugee, makeshift camps, slums and haor communities. 

Response 1: 

We appreciate the reviewer’s helpful suggestion to clarify potentially unfamiliar concepts early in the manuscript. We have revised the introduction to include brief definitions of “left-behind children,” “Rohingya refugees,” “makeshift camps,” “slums,” and “haor communities” in the highlighted paragraph on page 2 as follows:

Marginalized groups in Asia include slum communities under overcrowding, informal housing, poor sanitation, and limited public services. Haor communities in wetland areas of Bangladesh include residents who often disrupt healthcare access in flooding seasons. Rohingya refugees, a stateless Muslim minority displaced from Myanmar and living in often-overcrowded settlements. Makeshift camps refer to temporary, unregistered refugee shelters that lack formal infrastructure. And left-behind children, whose parents have migrated for work—often across borders or to urban areas—leaving children in the care of relatives or guardians, with inconsistent health service follow-up.

Comment 2: Type of review 
In the 2.1. Study selection section (methodology), it is indicated that "a narrative literature review" was carried out, also in line 162 "Given the narrative design of this review...". However, in the title, the summary or point 2.3. Search strategy is called "systematic review". Although it uses tools typical of a systematic review (such as PRISMA and inclusion/exclusion criteria), the analysis approach and presentation of results (mainly as a Thematic synthesis) is narrative. On the other hand, no formal quantitative evaluation has been carried out nor statistical aggregation criteria have been applied (typical of systematic reviews and/or meta-analyses), and diverse studies are included in terms of types and sources seeking breadth rather than statistical precision (in addition, this diversity makes a meta-analysis impossible, as the authors themselves acknowledge in line 146). Therefore, according to the latest trends, it is a narrative review with a systematic approach, also known as an integrative review; It would not be a "systematic review" as such. I recommend that the authors consider this change. 

Response 2: 

We fully agree with your assessment that the manuscript, while incorporating systematic techniques such as the PRISMA flowchart and predefined inclusion/exclusion criteria, is best categorized as a narrative review with a systematic approach, rather than a systematic review or meta-analysis.

We have made the following changes: 

Title has been revised to remove “Systematic Review.” The updated title now reads:

“Determinants of Parental Adherence to Childhood Immunization in Marginalized Under-Five Populations in Asia”

Abstract edited to change "systematic review" → "narrative review".

Section 2.1 (Study selection):

A new clarification sentence was added right after the heading:

“Although systematic search methods and PRISMA guidelines were used to enhance transparency and reproducibility, this review adopts a narrative design and thematic synthesis approach. No formal meta-analysis was performed due to heterogeneity of study types and outcomes.” (Page 2)

Section 2.3 (Search Strategy) updated:

The first sentence now begins with “This narrative review…” (Page 3)

Comment 3: Search process 

On the other hand, regarding the search process, it is stated that different sources were used to extract information: "bibliographic databases (PubMed, Scopus, Google Scholar) and organizational reports (WHO, UNICEF, Gavi, and DHS)". However, in the flowchart only PubMed, Scopus and Google Scholar appear as a source of eligible studies. What use did WHO, UNICEF, Gavi, and DHS have? If they were not source resources for the publications selected in this review, they should be deleted. 

Response 3: Thank you for this helpful observation. We confirm that while organizational sources (WHO, UNICEF, Gavi, DHS) were considered during preliminary scoping, they did not yield any eligible studies and were not used as sources for final inclusion. We have therefore removed them from the search description in Section 2.3 to accurately reflect the data sources used in this review. The PRISMA flowchart remains unchanged, as only bibliographic databases (PubMed, Scopus, and Google Scholar) contributed to included studies.

Comment 4: Data consistency 

The flowchart indicates that Google Scholar initially yielded 407 records. However, in table A1 of the appendix, "First 200 results screened" is indicated. This incongruity must be reviewed. 

Response 4: 

We thank you for identifying this important clarification. While Google Scholar generated 407 results using the search terms, we followed established guidance and precedent in screening only the first 200 results, as these are ranked by relevance and are most likely to yield eligible studies. We have updated the manuscript and supplementary file to clarify this:

In the PRISMA flowchart, we now state, “Google Scholar (407 results; first 200 screened).”

In Table A1, we clarified the note to read, “First 200 results screened (out of 407 retrieved).”

Comment 5: In the summary, I recommend numbering (1)...; 2)…) the five domains that influenced adherence.  

Response 5: We have added numbering in the conclusion as follows: Parental adherence to childhood immunization in marginalized Asian populations is shaped by (1) socioeconomic inequities, (2) trust and cultural beliefs, (3) migration vulnerabilities, (4) household dynamics, and (5) health system quality. (page 15)

Comment 6: In 2.2. Eligible criteria, line 90 presents the phrase "We excluded studies on adult immunization, non-Asian contexts, non-marginalized populations". Exclusion criteria are not the opposite of inclusion criteria. Therefore, this part of the sentence can be ignored. 

Response 6: We have revised the exclusion criteria in Section 2.2 to remove elements that are already covered implicitly by the inclusion criteria (e.g., non-Asian contexts and non-marginalized populations). We retained only those exclusions that are not directly derived from the inclusion scope, such as studies on adult immunization, clinical vaccine efficacy trials, and studies focusing exclusively on a single vaccine. This change improves clarity and avoids redundancy in the eligibility description. We highlight the rewritten sentence on page 3 as follows: We excluded studies on adult immunization, clinical vaccine efficacy trials, and studies focusing exclusively on a single vaccine (e.g., measles-only, polio-only).

Comment 7: Appendix B: It may be a file download error, but aren't the determinants "Trust & cultural beliefs"/"Health system & program" and "Household dynamics"/"Migration & mobility" also connected to each other? 

Response 7: 

Thank you for this insightful observation. Indeed, "Trust & cultural beliefs" often develop in response to experiences with the "Health system & program", and "Household dynamics" are frequently shaped by "Migration & mobility" — particularly in contexts involving transient populations or left-behind children. These interrelationships are conceptually acknowledged in our discussion.

However, in the revised Appendix B conceptual framework, we intentionally illustrate unidirectional arrows from each determinant directly toward Parental Adherence to Childhood Immunization. This visual design emphasizes that each thematic factor contributes independently and significantly to adherence decisions, regardless of secondary interactions. We chose not to include interconnecting arrows between determinant boxes in order to maintain clarity and focus the reader’s attention on the central outcome of interest. This decision reflects both conceptual parsimony and alignment with similar narrative review frameworks. The updated figure has now been included in Appendix B.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses an important and timely topic; determinants of parental adherence to childhood immunization among marginalized populations in Asia. The issue of vaccine equity and adherence in disadvantaged communities is highly relevant to global health priorities and aligns well with the aims of IJERPH. The paper is clearly written, logically structured, and synthesizes a diverse body of evidence. The thematic domains identified including socioeconomic and access inequities, trust and cultural beliefs, migration-related vulnerabilities, household dynamics, and health system capacity – are insightful and well-integrated.

However, while the manuscript is presented as a systematic review, the methodology does not currently fulfill the requirements for this classification. The search, screening, and appraisal processes do not fully align with the PRISMA 2020 or JBI standards for systematic reviews. For instance, the manuscript lacks a PROSPERO registration or protocol reference, which is essential for ensuring transparency and minimizing reporting bias. The PRISMA flow diagram, though mentioned, is not included, and details of study identification, exclusion, and inclusion criteria are insufficiently described.

Similarly, the search strategy requires greater transparency. While Boolean search terms are partially provided, the full search strings for each database and grey literature source are not presented. The description of grey literature retrieval from WHO, UNICEF, and Gavi is also incomplete – no specific search terms, time frames, or inclusion criteria are reported. These omissions make replication difficult and reduce confidence in the systematic nature of the review. Unless these aspects are comprehensively addressed, the paper is more accurately described as a narrative or scoping review rather than a systematic review.

Furthermore, the inclusion of previously published systematic reviews as part of the analyzed dataset is methodologically problematic unless this is clearly designed as an umbrella review. The current manuscript does not justify this decision or specify how such studies were integrated into the synthesis. The authors should clarify this point or remove secondary reviews from inclusion. The risk-of-bias assessment (Table A2) is a positive feature but would benefit from more explicit scoring, rationale, and discussion of how study quality influenced interpretation.

Despite these methodological limitations, the manuscript’s discussion and thematic synthesis are strong. The integration of findings across cultural and structural contexts offers meaningful policy insights. The analysis effectively highlights persistent inequities and the role of trust and systemic barriers in shaping immunization outcomes. However, to meet the standards of a systematic review, substantial revisions are required. The authors are encouraged either to (1) fully revise the manuscript to comply with PRISMA standards (including PROSPERO registration, complete search transparency, and inclusion/exclusion documentation), or (2) reframe the paper as a narrative review with a strong conceptual synthesis, which would still represent a valuable scholarly contribution.

In summary, this is a well-conceived and relevant paper with clear potential to contribute to the literature on immunization equity. Nonetheless, the methodological inconsistencies preclude its acceptance as a systematic review in its current form. I recommend major revision, with particular attention to clarifying review type, ensuring full methodological transparency, and aligning reporting with appropriate review standards.

Author Response

Comment 1: The manuscript is presented as a systematic review, the methodology does not currently fulfill the requirements for this classification. The search, screening, and appraisal processes do not fully align with the PRISMA 2020 or JBI standards for systematic reviews. For instance, the manuscript lacks a PROSPERO registration or protocol reference, which is essential for ensuring transparency and minimizing reporting bias. The PRISMA flow diagram, though mentioned, is not included, and details of study identification, exclusion, and inclusion criteria are insufficiently described.

Response 1: We sincerely thank you for the positive assessment of the manuscript’s significance, structure, and thematic contributions. We have reclassified the manuscript as a narrative review rather than a systematic review. The following revisions were made to address these concerns:

The title, abstract, methods, and discussion sections have been updated to clearly reflect the narrative review design.

References to “systematic review” and associated frameworks (e.g., PRISMA, PROSPERO) have been removed or reframed to align with a narrative synthesis approach.

We retained a PRISMA-style flow diagram for transparency in reporting the search and screening process, though it is used here as a reporting tool rather than a claim of systematic rigor.

Section 2.1 and 2.3 have been revised to clarify the study selection, search strategy, and inclusion/exclusion criteria, now aligned with narrative review methodology.

Studies included in the synthesis are presented thematically, and no formal meta-analysis or quantitative appraisal has been performed, in line with narrative synthesis standards.

Comment 2: Similarly, the search strategy requires greater transparency. While Boolean search terms are partially provided, the full search strings for each database and grey literature source are not presented. The description of grey literature retrieval from WHO, UNICEF, and Gavi is also incomplete – no specific search terms, time frames, or inclusion criteria are reported. These omissions make replication difficult and reduce confidence in the systematic nature of the review. Unless these aspects are comprehensively addressed, the paper is more accurately described as a narrative or scoping review rather than a systematic review.

Response 2: In response, we have made the following changes:
The manuscript has been reframed as a narrative review, and no longer claims to be a systematic review.
All references to systematic methods (e.g., PRISMA compliance, grey literature inclusion) have been revised or removed to accurately reflect the study’s design and scope.
As part of this change, the previously mentioned grey literature sources (WHO, UNICEF, Gavi, and DHS) were removed from the search strategy in Section 2.3, as they did not yield included studies and no formal or reproducible search protocol was used for those platforms.

Comment 3: Furthermore, the inclusion of previously published systematic reviews as part of the analyzed dataset is methodologically problematic unless this is clearly designed as an umbrella review. The current manuscript does not justify this decision or specify how such studies were integrated into the synthesis. The authors should clarify this point or remove secondary reviews from inclusion. The risk-of-bias assessment (Table A2) is a positive feature but would benefit from more explicit scoring, rationale, and discussion of how study quality influenced interpretation.

Response 3: We thank you for raising this methodological issue. We acknowledge that the inclusion of systematic reviews within the analyzed dataset requires clear justification and distinction from the synthesis of primary studies. We have retained a small number of relevant systematic reviews that met our inclusion criteria, not as primary data, but to provide contextual insights or thematic reinforcement where appropriate. These reviews were not included in thematic coding or risk-of-bias assessment and were not counted in the total number of primary studies synthesized. A new clarifying paragraph has been added to the end of Section 2.3 to state:Two included studies were themselves systematic reviews. These were not integrated into the thematic synthesis alongside primary studies. Instead, they were retained for context and triangulation. Findings from these reviews were cited descriptively where relevant but were not used to identify or code determinants. No data were duplicated from primary studies already included.

Adding footnote in Table A2/Supplementary: Note: The two systematic reviews included (Kalaij et al., 2021; Novilla et al., 2023) were appraised for general quality and transparency but were not thematically synthesized. Only primary studies informed the thematic domains.

In Section 2.5. Risk of bias and quality assessment, we have added "Only primary studies included in thematic synthesis were appraised for risk of bias". 

In the discussion, last section: we added, "Study quality was considered in interpreting the results. Findings from studies rated as lower quality (e.g., lacking clarity in methods or sampling) were interpreted with caution and weighed less heavily in the synthesis of themes. Two retained systematic reviews served a supplementary role. Their findings were referenced contextually but did not inform the thematic structure or determinant mapping to avoid duplication bias".

Comment 4: Despite these methodological limitations, the manuscript’s discussion and thematic synthesis are strong. The integration of findings across cultural and structural contexts offers meaningful policy insights. The analysis effectively highlights persistent inequities and the role of trust and systemic barriers in shaping immunization outcomes. However, to meet the standards of a systematic review, substantial revisions are required. The authors are encouraged either to (1) fully revise the manuscript to comply with PRISMA standards (including PROSPERO registration, complete search transparency, and inclusion/exclusion documentation), or (2) reframe the paper as a narrative review with a strong conceptual synthesis, which would still represent a valuable scholarly contribution.

Response 4: Thank you for encouraging feedback on the value and thematic strength of the manuscript. In line with the reviewer’s recommendation, we have chosen to reframe the manuscript as a narrative review. As such, the concerns related to PROSPERO registration, PRISMA compliance, and the formal structure of systematic reviews no longer apply. We have made corresponding changes throughout the manuscript:
The title, abstract, and methodology sections (Sections 1 and 2) have been revised to explicitly reflect the narrative review design.
The revised version emphasizes conceptual synthesis rather than methodological standardization, while maintaining transparency in study selection and thematic mapping.

Reviewer 3 Report

Comments and Suggestions for Authors

1. In your uploaded manuscript, the authors state in several places that the review was conducted “following PRISMA guidelines” and describe it as a “systematic review.”
   However, when reading through the Methods and Results sections, the work clearly blends features of a narrative review rather than a fully systematic one. 

   Lines 61–63 mentions that We conducted a narrative literature review of studies published between 2015 and 2025...”

   This contradicts the title and abstract that call it a systematic review.

   A systematic review normally provides structured quality appraisal tables, quantitative summary metrics (or at least clear scoring), and a PRISMA checklist. Here it’s descriptive only.
2. The manuscript does not mention PROSPERO or OSF registration either. This is a requirement.
3. The definition of marginalized populations is broad. Please justify why Western Asia was excluded while some Southeast Asian refugee groups were included. A map or table of geographic distribution would improve clarity
4. Indicate whether quality assessment was performed independently by at least two reviewers. If so, describe how discrepancies were resolved (e.g., through consensus or involvement of a third reviewer). If not, acknowledge this as a limitation.
5. The description of the thematic synthesis reads as mainly descriptive. Please explain more clearly how themes were identified (for example, using a specific coding approach like a thematic framework) and include a few short quotes from qualitative studies to support the themes.
6. Some sentences suggest causation, but most of the included studies are cross-sectional. Please rephrase these to show association rather than cause and effect.
7. In the discussion, the terms “coverage” and “adherence” are sometimes used as if they mean the same thing. Clarify the difference: coverage refers to the health system’s performance, while adherence refers to the caregiver’s behavior.
8. The reference list is good, but it would benefit from adding recent global policy documents

Author Response

Comment 1: In your uploaded manuscript, the authors state in several places that the review was conducted “following PRISMA guidelines” and describe it as a “systematic review.”
However, when reading through the Methods and Results sections, the work clearly blends features of a narrative review rather than a fully systematic one. Lines 61–63 mentions that We conducted a narrative literature review of studies published between 2015 and 2025...”This contradicts the title and abstract that call it a systematic review.
A systematic review normally provides structured quality appraisal tables, quantitative summary metrics (or at least clear scoring), and a PRISMA checklist. Here it’s descriptive only.
The manuscript does not mention PROSPERO or OSF registration either. This is a requirement.

Response 1: Thank you for your comments and for identifying the inconsistencies in terminology and methodology between the title, abstract, and methods sections. In response, we have now:
Reframed the manuscript as a narrative review across all sections, including the title, abstract, methods, and discussion.
Removed all references to PRISMA or systematic review classification, and clarified that no PROSPERO or OSF registration was performed.
Revised the methods to emphasize the narrative thematic synthesis approach, without implying a formal systematic process.
Retained a flow diagram to improve transparency but clarified that it is for descriptive purposes and not part of a PRISMA-compliant protocol. We add the note under Figure 1. The PRISMA flow diagram describing the study selection process as follows: 

Note: This flow diagram follows PRISMA-style formatting for transparency but reflects procedures adapted to a narrative literature review.

Clarified in the quality appraisal table (Table A2/Supplementary) that only primary studies were assessed, and results were used qualitatively to support cautious interpretation.

Comment 2: The definition of marginalized populations is broad. Please justify why Western Asia was excluded while some Southeast Asian refugee groups were included. A map or table of geographic distribution would improve clarity.

Response 2: Thank you for this suggestion. We have added a clearer definition of marginalized populations on page 2 of the manuscript: Marginalized groups in Asia include slum communities under overcrowding, informal housing, poor sanitation, and limited public services. Haor communities in wetland areas of Bangladesh include residents who often disrupt healthcare access in flooding seasons. Rohingya refugees, a stateless Muslim minority displaced from Myanmar and living in often-overcrowded settlements. Makeshift camps refer to temporary, unregistered refugee shelters that lack formal infrastructure. And left-behind children, whose parents have migrated for work—often across borders or to urban areas—leaving children in the care of relatives or guardians, with inconsistent health service follow-up.

Regarding the geographic scope, Western Asia was excluded to maintain regional focus and contextual coherence. The majority of immunization inequities explored in this review relate to health system structures, sociopolitical dynamics, and community-level determinants that are relatively more comparable within South and Southeast Asian contexts. Western Asia, in contrast, presents:
Distinct health governance frameworks (often centralized or conflict-affected),
Differing geopolitical histories of marginalization (e.g., conflict zones, occupation, sanctions),
And differing patterns of childhood immunization coverage reporting and availability.
Including Western Asia would have expanded the scope considerably and introduced heterogeneity that may have limited thematic cohesion. In contrast, refugee and internally displaced populations within South and Southeast Asia (e.g., Rohingya, slum populations, left-behind children) were included because they reflect intra-regional vulnerabilities and fall within the immunization systems of the target countries. We add Geographic scope of selected studies in Section 2.1 page 2 as follows: 

Geographic scope of selected studies: this review focuses on marginalized populations within South and Southeast Asia, where disparities in childhood immunization coverage are most pronounced due to intersecting social, economic, and health system barriers. Countries represented in the included studies include India, Bangladesh, Nepal, Pakistan, Myanmar, Indonesia, Vietnam, Cambodia, and the Philippines. Refugee and displaced populations such as the Rohingya (from Myanmar, residing in Bangladesh), urban slum dwellers, and left-behind children of migrant workers are considered within the national and subnational contexts of these countries. Western Asia was excluded to maintain regional coherence, as the sociopolitical drivers of marginalization and immunization system structures differ substantially. Inclusion would have introduced heterogeneity that limits comparative synthesis across themes. We have also inserted Figure B2 in the supplementary with a map to clarify countries included in the review.

Comment 3: Indicate whether quality assessment was performed independently by at least two reviewers. If so, describe how discrepancies were resolved (e.g., through consensus or involvement of a third reviewer). If not, acknowledge this as a limitation.

Response 3: We appreciate the reviewer’s attention to the transparency of the quality assessment process. As noted in Section 2.4: Data Extraction and Analysis, two independent reviewers conducted data extraction and quality appraisal for all included studies.
Any discrepancies between the reviewers were resolved through discussion and consensus, and when needed, a third senior author adjudicated disagreements. This process ensured consistency in the assessment of study relevance and quality. We have retained this clarification in Section 2.4 and trust that it now addresses the concern.

Comment 4: The description of the thematic synthesis reads as mainly descriptive. Please explain more clearly how themes were identified (for example, using a specific coding approach like a thematic framework) and include a few short quotes from qualitative studies to support the themes.

Response 4: We have added a short paragraph to mention the inductive–deductive approachfor developing themes:

A narrative thematic synthesis was conducted to identify recurring determinants of parental adherence across included studies. Themes were developed through an inductive–deductive approach, combining a priori coding (based on the research objectives and literature) with emergent codes identified during full-text review. Coded segments were clustered into five overarching thematic domains:
(1) Socioeconomic and access inequities,
(2) Trust, cultural beliefs and social norms,
(3) Migration, refugee, and mobility-related vulnerabilities,
(4) Household and caregiver dynamics, and
(5) Health system and program.

Representative codes and illustrative quotes from qualitative studies are presented in Table 3 to support transparency and contextual insight .Table 3. Representative codes and illustrative quotes supporting thematic domains

Comment 5: Some sentences suggest causation, but most of the included studies are cross-sectional. Please rephrase these to show association rather than cause and effect.

Response 5: We agree that most included studies are either cross-sectional or qualitative in nature and therefore do not support strong causal inference. In response, we have systematically reviewed the manuscript and revised all statements that previously implied causality. Replaced causal terms such as “influenced,” “due to,” “resulted in,” and “led to” with more appropriate associative language such as “were associated with,” “linked to,” or “commonly reported as barriers/facilitators.” The following updated phrasing is as follows:

Abstract: Five domains were associated with adherence.....

3.2.3. Migration, refugee, and mobility-related vulnerabilities .

In Vietnam’s border regions, minority children had extremely low adherence (18.9%), which was associated with structural barriers and low parental self-efficacy [4].

4.1. Principal findings

Parental decisions regarding childhood immunization were shaped by trust, cultural beliefs, and prevailing social norms

Household and caregiver dynamics were important contextual factors. Fathers, grandmothers, and community leaders were often reported to play key roles in parental decision-making.

Larger household size, birth order, and maternal employment status were also associated with immunization uptake.

Facility readiness, staffing, provider communication, and follow-up systems were frequently associated with immunization inequities

4.2. Comparison with Prior Reviews

Similarly, possession of an EPI card was consistently associated with improved adherence, highlighting the role of programmatic design

Comment 6: In the discussion, the terms “coverage” and “adherence” are sometimes used as if they mean the same thing. Clarify the difference: coverage refers to the health system’s performance, while adherence refers to the caregiver’s behavior.

Response 6: Thank you for this important observation. We agree that “coverage” and “adherence” reflect distinct but related concepts. In response, we have clarified their definitions in the Discussion section:
Coverage typically refers to the proportion of children who have received a particular vaccine, and is often used as a performance indicator of the health system.
Adherence, in contrast, reflects the caregiver’s compliance with the recommended immunization schedule, especially the timeliness and completion of all required doses within the specified age windows.
A child may be fully vaccinated (high coverage) but not receive doses at the recommended intervals (low adherence), potentially compromising immune protection.
We have revised the relevant sentences in the discussion to reflect this conceptual distinction.
Suggested Clarifying Sentence for section 4.2: Comparison with Prior Reviews

In this review, "coverage" refers to the proportion of children who received vaccinations, commonly used as a health system performance indicator. "Adherence", on the other hand, refers to caregivers’ timely compliance with the recommended vaccination schedule—capturing not just whether vaccines were received, but also whether they were administered at the appropriate ages and intervals.

Comment 7: The reference list is good, but it would benefit from adding recent global policy documents

Response 7: Thank you for this valuable suggestion. We acknowledge the importance of integrating relevant global policy frameworks. However, as this review primarily synthesizes peer-reviewed empirical studies focused on determinants of parental adherence among marginalized populations in Asia, our inclusion criteria prioritized original research published in academic journals.
We initially included select organizational reports (e.g., WHO, UNICEF, Gavi) as background sources during the search process, but ultimately did not cite them directly in the synthesis due to:
Their general global focus, which did not offer Asia-specific determinants of adherence.
Their classification as grey literature, which was outside the formal scope of included sources to maintain consistency in methodological rigor and reproducibility.
The emphasis on including studies with empirical data—particularly qualitative or cross-sectional findings—from marginalized populations.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for addressing my comments and for converting the paper to a narrative review. As a narrative review paper, you have the liberty to include any paper as you may wish, but of course, being systematic in your approach will be a plus. While there are statements within the body of the paper justifying the exclusion of systematic reviews from your synthesis, that may no longer be required, as the paper type has changed. I hope you can have a quick review of the weave, the content seamlessly and improve the flow. 

Author Response

Comment 1: 

We sincerely thank the reviewer for the constructive and encouraging feedback throughout the review process. We appreciate your recognition of our efforts to reframe the manuscript as a narrative review.
In response to this final comment:
We agree that justifications for excluding systematic reviews are no longer necessary under the narrative review framework. Accordingly, we have revised the relevant sections (Methods and Results) to remove redundant statements about excluding systematic reviews.
To improve the coherence and flow, we carefully reread and revised transitions and phrasing across sections. Our goal was to ensure that the thematic synthesis reads more fluidly and that the integration of findings across studies appears seamless.
Although the review is now narrative in type, we retained structured methods (e.g., search strategy, inclusion criteria, and quality appraisal) to maintain transparency and credibility in line with best practices for narrative synthesis.
We are grateful for your thoughtful input, which helped strengthen both the methodological clarity and narrative presentation of this review.

Response 1: 

We sincerely thank the reviewer for the constructive and encouraging feedback throughout the review process. We appreciate your recognition of our efforts to reframe the manuscript as a narrative review.
In response to this final comment:
We agree that justifications for excluding systematic reviews are no longer necessary under the narrative review framework. Accordingly, we have revised the relevant sections (Methods and Results) to remove redundant statements about excluding systematic reviews.
To improve the coherence and flow, we carefully reread and revised transitions and phrasing across sections. Our goal was to ensure that the thematic synthesis reads more fluidly and that the integration of findings across studies appears seamless.
Although the review is now narrative in type, we retained structured methods (e.g., search strategy, inclusion criteria, and quality appraisal) to maintain transparency and credibility in line with best practices for narrative synthesis.
We are grateful for your thoughtful input, which helped strengthen both the methodological clarity and narrative presentation of this review.

 

Reviewer 3 Report

Comments and Suggestions for Authors

All the comments of the first round have been satisfactorily addressed

Author Response

Comment 1: All the comments of the first round have been satisfactorily addressed.

Response 1: Thank you for your encouragement