Review Reports - Peste Des Petits Ruminants in Pakistan: Current Status, Challenges and Prospects for Vaccine Development

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a literature review on aspects of Peste des Petits Ruminants (PPR) virus infection, relevant to disease control.

The manuscript addresses the following topics: epidemiology (Paragraph 2), diagnosis (3), existing vaccines and their limitations (4), recent advances in vaccine research and development (5), thermostable formulations (6), novel delivery methods (7) and current and potential strategies for vaccine deployment (8).

The literature search and presentation are comprehensive and well-structured. While paragraphs 2 and 3 provide detailed scientific information, with a specific focus on the epidemiology and diagnosis of PPR in Pakistan data specific to this country are almost completely absent in the following sections on vaccines and vaccination strategies (Para 4–8), probably reflecting a lack of available data in these areas.

The limited information on PPR in Pakistan, combined with a weak analysis, results in unclear identification of gaps in disease control and consequently, the suggestions proposed are generic and lack specificity. For these reasons, I unfortunately cannot recommend this manuscript for publication in its current form.

Minor Comments:

A) Figures 1 and 2:

The figures are not mentioned in the text.
The sources of data are not indicated in the legends.

B) Table 1:

The table is not mentioned and integrated into the text.
Its placement at the end of paragraph 8 is unclear.
The table should be introduced with background information for clarity and relevance

Author Response

Major Comments

Reviewer Comment: This manuscript presents a literature review on aspects of Peste des Petits Ruminants (PPR) virus infection, relevant to disease control. The literature search and presentation are comprehensive and well-structured. While paragraphs 2 and 3 provide detailed scientific information, with a specific focus on the epidemiology and diagnosis of PPR in Pakistan data specific to this country are almost completely absent in the following sections on vaccines and vaccination strategies (Para 4–8), probably reflecting a lack of available data in these areas. The limited information on PPR in Pakistan, combined with a weak analysis, results in unclear identification of gaps in disease control and consequently, the suggestions proposed are generic and lack specificity. For these reasons, I unfortunately cannot recommend this manuscript for publication in its current form.

Response: We appreciate the reviewer's acknowledgement of the comprehensive and well-structured nature of the review. We recognize the initial deficiency regarding country-specific data in the sections on vaccines and strategies (originally paragraphs 4-8). To address this critical concern and provide a more focused and Pakistan-specific analysis, we have undertaken significant revisions:

New Sections on National Strategy and Comparative Aspects: We have inserted two new sections, "Pakistan's National PPR Control Programme" (Section 4) and "Comparative Aspects of PPR Vaccination in Sheep and Goats" (Section 6). These sections specifically detail Pakistan's current control stage, its risk-based and targeted vaccination strategies, the use of the Nigeria 75/1 vaccine, and the operational challenges it faces.
Integration of Local Vaccine Research and Field Data: We have substantially revised and expanded the remaining sections (Section 5, 7, 9, 10, 12) to incorporate local Pakistani research, field trial data, and institutional capacity for vaccine development.

- Section 5 (PPR Vaccination Strategies and Progress in Pakistan): Now includes details on the locally produced Nigeria 75/1 vaccine, suboptimal national coverage (35–45%), and the role of the Veterinary Research Institute (VRI), Lahore.
- Section 7 (Recent advances in vaccine research and development): Emphasizes that Pakistani research at UVAS and NVL is guided by the endemic Lineage IV strain and highlights promising local recombinant vaccine candidates (e.g., UVAS-developed candidates with 100% protection).
- Section 9 (Thermostable formulations): Now features the success of locally evaluated thermostable Nigeria 75/1 preparations under Sindh's semi-arid conditions and validates it as a key tool for Pakistan's program.

- Section 12 (Current and potential strategies for vaccine deployment): Links mass, targeted, and ring vaccination strategies directly to Pakistan's diverse husbandry systems and identifies the specific logistical constraints that novel methods could solve (e.g., targeting border regions, nomadic herds).

Minor Comments

A) Figures 1 and 2: The figures are not mentioned in the text. The sources of data are not indicated in the legends.

Response: The figures have been integrated into the text, and the sources of data are now clearly indicated in the revised legends. (Figure 1 mentioned in the text line no.105, and Figure 2 mentioned in the text line no. 121

B) Table 1: The table is not mentioned and integrated into the text. Its placement at the end of paragraph 8 is unclear. The table should be introduced with background information for clarity and relevance.

Response: Thanks for this suggestion. Table 1 (originally at the end of the unrevised PPR research section) has been split and re-positioned for clarity and is now properly introduced and integrated into the text (Line 316)

Reviewer 2 Report

Comments and Suggestions for Authors

This is an excellent manuscript about vaccines and vaccination in PPR.

The authors have reviewed the relevant literature and have made a fantastic work to summarise all relevant information.

There are just some points that require improvement.

The manuscript should make use of tables to summarise the relevant papers, which will allow future readers to be able to go deeper into the meaning of the paper.
The manuscript must include a new section to explain differences between sheep and goats in their vaccination.
The manuscript should include a new section with the prospects for commercial preparation of vaccines.
The manuscript should include a list of all patented vaccines against the infection worldwide.
The manuscript should include a larger number of references, given the importance of the topic. I expect at least 150 references. Also, the number of references from Africa must increase.
The manuscript should conclude with a clear take home message regarding the future of vaccination in PPR.

In all, an excellent submission that merits acceptance after making the above few changes.

Author Response

Reviewer Comment: This is an excellent manuscript about vaccines and vaccination in PPR. The authors have reviewed the relevant literature and have made a fantastic work to summarise all relevant information. There are just some points that require improvement.

Response: We are delighted to receive such positive feedback and thank the reviewer for the encouraging words and constructive suggestions. We have implemented all requested changes to further strengthen the manuscript.

Reviewer Comment: The manuscript should make use of tables to summarise the relevant papers, which will allow future readers to be able to go deeper into the meaning of the paper.

Response: We agree that comprehensive tables significantly enhance clarity and utility. We have implemented this change by including two distinct tables that summarize the most critical data points in the review.

Table 1: Diagnostic Results of PPR (2019-2024): This table is introduced at the end of the Epidemiology section and consolidates major serological and molecular studies on PPR prevalence across Pakistani provinces, including sample sizes, positive cases, and diagnostic methods.
Location of introduction: Lines 316
Table 2: Global and Regional Advancements in PPR Vaccine Research: This table summarizes comparative data on different vaccine types, target species, key outcomes, and limitations, including Pakistan's contributions. (Line 452)

Reviewer Comment: The manuscript must include a new section to explain differences between sheep and goats in their vaccination.

Response: We have incorporated a new section dedicated to the comparative aspects of PPR vaccination in sheep and goats, which is essential given the different susceptibilities and immune responses in the field.

New Section 6: Comparative Aspects of PPR Vaccination in Sheep and Goats has been added. This section discusses the higher susceptibility of goats (up to 80% mortality in naïve herds) compared to sheep (10-40% mortality) and notes the different immune responses, suggesting goats may require more frequent booster vaccinations and be the focus of seromonitoring.
Location of new text: Lines 263-276

Reviewer Comment: The manuscript should include a new section with the prospects for commercial preparation of vaccines.

Response: A new section addressing the transition from laboratory candidates to commercial production has been included.

New Section 8: Prospects and Challenges for the Commercial Production of PPR Vaccines is now included. This section discusses challenges such as scale-up, cost-effectiveness, stringent Good Manufacturing Practice (GMP) conditions, and the role of the existing local production capacity (e.g., at VRI, Lahore) for technology transfer. (Line 317-336)

Reviewer Comment: The manuscript should include a list of all patented vaccines against the infection worldwide.

Response: We have added a new section, Section 11: Intellectual Property Landscape, which specifically addresses the global PPR vaccine patent landscape, noting the progression from conventional live-attenuated vaccines to next-generation thermostable, DIVA-compatible, and DNA-based platforms. While providing an exhaustive, real-time list of all patents is beyond the scope of a review, this new section highlights the key technological areas being protected.

Location of new text: Lines 389-393

Reviewer Comment: The manuscript should include a larger number of references, given the importance of the topic. I expect at least 150 references. Also, the number of references from Africa must increase.

Response: We have conducted a thorough search and significantly expanded the reference list in the revised manuscript to meet the reviewer's expectations, including an increased focus on African sources.

Reviewer Comment: The manuscript should conclude with a clear take-home message regarding the future of vaccination in PPR.

Response: The conclusion (Section 13) has been revised to provide a clear, strong, and concise take-home message, focusing on the need for Pakistan to strategically transition to next-generation (thermostable and DIVA-compatible) vaccines, leverage its VRI infrastructure, and ensure sustained political and financial commitment to achieve the 2030 eradication goal.

Location of revised text: Lines 456-474

Reviewer 3 Report

Comments and Suggestions for Authors

The reference formats are inconsistent, and some references are inaccessible to me. Please unify the format and provide specific retrieval information to facilitate access.

PPRV has been affecting not only Asia and Africa but has also been prevalent in some European countries in recent years. The description of its epidemiological distribution in the Introduction should be refined accordingly.

According to the author's description, lineage III of PPRV has been detected in some provinces of Pakistan. However, the cited references do not contain relevant conclusions supporting this claim. Furthermore, to the best of my knowledge, most Asian countries only have lineage IV of the virus in circulation. The author should provide concrete references to substantiate the presence of lineage III in the country.

To reach the standards for publication, this paper still requires in-depth revisions to its content.

The title of this paper focuses on the epidemiological situation of PPR in Pakistan. However, most contents are discussed from a broader perspective. For instance, in vaccine part, I believe the author should provide a more detailed description of the measures taken by Pakistan to combat PPR. What is the country's vaccination strategy? Are there any relevant research advancements regarding vaccines in Pakistan? Has the vaccination strategy been effective in providing protection? What is the incidence rate of PPR in the country? Regarding the control of PPR, the author should provide a detailed account of the specific control strategies implemented by the country, how risk areas are delineated, and the control measures adopted in different risk zones. Additionally, at which stage is the country currently positioned in the PPR eradication program? In summary, the aforementioned sections are described too broadly. The author should elaborate based on the country's actual situation rather than speaking in general terms.

Similarly, in Section 9, I suggest that the author elaborate on the content rather than simply listing points.

Author Response

Reviewer Comment: The reference formats are inconsistent, and some references are inaccessible to me. Please unify the format and provide specific retrieval information to facilitate access.

Response: We apologize for the initial inconsistency in the reference formats and any accessibility issues. We have thoroughly reviewed and standardized the format of all references to ensure a uniform presentation throughout the manuscript.

Reviewer Comment: PPRV has been affecting not only Asia and Africa but has also been prevalent in some European countries in recent years. The description of its epidemiological distribution in the Introduction should be refined accordingly.

Response: We have revised the description of the PPRV epidemiological distribution in the Introduction (Section 1) to accurately reflect the global spread of the prevalent lineage.

The text in the introduction has been updated to state that Lineage IV is the most widespread and prevalent, affecting countries in Africa, the Middle East, and Asia. This accurately covers the highly endemic regions and aligns with the focus of the review.

Reviewer Comment: According to the author's description, lineage III of PPRV has been detected in some provinces of Pakistan. However, the cited references do not contain relevant conclusions supporting this claim. Furthermore, to the best of my knowledge, most Asian countries only have lineage IV of the virus in circulation. The author should provide concrete references to substantiate the presence of lineage III in the country.

Response: We appreciate the reviewer pointing out this critical inaccuracy. Upon re-examination of the literature, we concur that the reported endemic strain in Pakistan is overwhelmingly Lineage IV, and the claim regarding the presence of Lineage III was unsubstantiated by the concrete references we provided. We have therefore removed all mention of Lineage III from the manuscript to maintain scientific accuracy. The revised text correctly emphasizes that:

Lineage IV is the predominant and widespread strain in Pakistan, affecting all provinces and regions.
Phylogenetic analysis confirms that Pakistani isolates cluster into two distinct subgroups within Lineage IV (IVa and IVb).
All vaccine development and surveillance discussions are now correctly framed around the endemic Lineage IV virus.

Reviewer Comment: The title of this paper focuses on the epidemiological situation of PPR in Pakistan. However, most contents are discussed from a broader perspective. For instance, in vaccine part, I believe the author should provide a more detailed description of the measures taken by Pakistan to combat PPR. What is the country's vaccination strategy? Are there any relevant research advancements regarding vaccines in Pakistan? Has the vaccination strategy been effective in providing protection? What is the incidence rate of PPR in the country? Regarding the control of PPR, the author should provide a detailed account of the specific control strategies implemented by the country, how risk areas are delineated, and the control measures adopted in different risk zones. Additionally, at which stage is the country currently positioned in the PPR eradication program? In summary, the aforementioned sections are described too broadly. The author should elaborate based on the country's actual situation rather than speaking in general terms.

Response: We fully agree with the need to focus the content specifically on Pakistan's situation to align with the title and provide high-impact, country-specific information. We have undertaken substantial revisions across multiple sections to address this by moving away from general descriptions to detailed accounts of Pakistan's efforts:

Stage in Eradication Program: We have explicitly stated Pakistan's current position.
- Pakistan is currently positioned in Stage 2 (Risk Reduction) of the Progressive Control Pathway (PGRP) for PPR.
Specific Control Strategies and Risk Delineation: We have added a new dedicated section, Section 4: Pakistan's National PPR Control Programme.
- The section explains that the strategy is based on delineation of risk zones using factors like recurrent outbreaks, proximity to endemic borders (Afghanistan and Iran), and small ruminant density along trade routes.
- The primary control measure in these zones is targeted vaccination campaigns using the Nigeria 75/1 vaccine.
- The section details the immediate response to outbreaks, which involves quarantine and ring vaccination.
Vaccination Strategy and Efficacy: Section 5 (PPR Vaccination Strategies and Progress in Pakistan) now provides specifics.
- The strategy employs the live-attenuated Nigeria 75/1 strain, locally produced by the Veterinary Research Institute (VRI), Lahore.
- It specifies the use of annual mass vaccination campaigns targeting high-risk districts in Sindh, Punjab, and Khyber Pakhtunkhwa.
- The section highlights that national immunization coverage remains suboptimal, averaging 35–45% of the small ruminant population.
- Efficacy is supported by local evaluations of thermostable Nigeria 75/1 preparations that retained full protective efficacy after exposure to for up to 14 days under semi-arid conditions.
Local Research Advancements: Section 7 (Recent advances in vaccine research and development) is now focused on Pakistani initiatives.
- It highlights leading institutions like the University of Veterinary and Animal Sciences (UVAS) and the National Veterinary Laboratories (NVL).
- It details the focus on developing second-generation vaccines tailored to the endemic Lineage IV strains.
- It cites preliminary studies on a UVAS-developed recombinant candidate vaccine that demonstrated a 100% protection rate in goats.
PPR Incidence Rate: The manuscript includes extensive data on prevalence, which is a better measure than incidence for a broad review.
- The national level serological survey from 2014 showed a true seroprevalence of 48.5% for PPR in Pakistan.
- Table 1 provides a detailed breakdown of positive sample counts across various regions and species from 2019 to 2024, offering a measure of recent disease activity.

Reviewer Comment: Similarly, in Section 9, I suggest that the author elaborate on the content rather than simply listing points.

Response: Section 9 (Thermostable formulations) has been significantly expanded and elaborated to move beyond a simple list. The revised section now provides:

- Rationale for Pakistan: It clearly states that thermostable vaccines are a transformative advantage for Pakistan due to challenging geography and infrastructure limitations that hinder cold chain maintenance.
- Specific Pakistani Example: It highlights the thermostable live-attenuated Nigeria 75/1 vaccine and cites its proven high safety, immunogenicity, and efficacy in Pakistani field trials.
- Strategic Deployment: It explicitly recommends the prioritized deployment of this validated vaccine in logistically challenging regions like Balochistan and Khyber Pakhtunkhwa.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

All the issues were addressed. I recommend acceptance.

Author Response

Dear Reviewer (2),

Thank you very much for your final assessment and for recommending our manuscript for acceptance.

We are delighted that you found all issues were adequately addressed. Your insightful comments during the initial review were invaluable in helping us improve the paper.

We appreciate your time and expertise.

Reviewer 3 Report

Comments and Suggestions for Authors

After careful review, I still believe this article does not meet the requirements for publication. The authors did not fully and carefully revise the manuscript according to the reviewers' comments. The majority of the content consists of established knowledge, offering little new insight for readers. The article fails to focus specifically on the national context of Pakistan and remains overly general in its discussion.

Author Response

Dear Reviewer 3,

Thank you for taking the time to review our manuscript and for providing your further feedback. We have carefully studied your comments and have undertaken a significant and careful revision of the manuscript to address the concerns you raised.

Reviewer Comment 1	Response:
The reference formats are inconsistent, and some references are inaccessible to me. Please unify the format and provide specific retrieval information to facilitate access.	Thank you for your observation. The reference section has been completely revised and reformatted according to the MDPI reference style. All references now include authors’ full names, publication year, full journal titles (not abbreviations), volume, and page numbers. Where applicable, DOI links have been added to facilitate easy retrieval and verification.
PPRV has been affecting not only Asia and Africa but has also been prevalent in some European countries in recent years. The description of its epidemiological distribution in the Introduction should be refined accordingly.	We appreciate this valuable suggestion. The Introduction section has been revised to reflect the updated global epidemiological distribution of PPRV. We have now included references and examples of recent detections in European regions, such as Turkey, Georgia, and Bulgaria, which represent the transboundary expansion of PPR from Asia into southeastern Europe
According to the author’s description, lineage III of PPRV has been detected in some provinces of Pakistan. However, the cited references do not contain relevant conclusions supporting this claim. Furthermore, to the best of my knowledge, most Asian countries only have lineage IV of the virus in circulation. The author should provide concrete references to substantiate the presence of lineage III in the country.	We thank the reviewer for this helpful comment. After reviewing the information again, we found that there is no confirmed molecular evidence showing the presence of PPRV lineage III in Pakistan. All available studies report that only lineage IV is found in Pakistan and nearby countries. We have corrected the statement about lineage III to make sure there is no misunderstanding.
To reach the standards for publication, this paper still requires in-depth revisions to its content.	We sincerely appreciate this insightful remark and have undertaken an extensive revision of the manuscript to enhance its clarity, accuracy, and analytical depth. The revised version now incorporates detailed, country-specific information, particularly outlining Pakistan’s national control framework, vaccination strategies, surveillance mechanisms, and PPR risk zoning. Furthermore, the manuscript’s structure and language have been refined to achieve greater scientific rigor, coherence, and precision
The title of this paper focuses on the epidemiological situation of PPR in Pakistan. However, most contents are discussed from a broader perspective. For instance, in the vaccine part, I believe the author should provide a more detailed description of the measures taken by Pakistan to combat PPR. What is the country’s vaccination strategy? Are there any relevant research advancements regarding vaccines in Pakistan? Has the vaccination strategy been effective in providing protection? What is the incidence rate of PPR in the country? Regarding the control of PPR, the author should provide a detailed account of the specific control strategies implemented by the country, how risk areas are delineated, and the control measures adopted in different risk zones. Additionally, at which stage is the country currently positioned in the PPR eradication program? In summary, the aforementioned sections are described too broadly. The author should elaborate based on the country’s actual situation rather than speaking in general terms.	We sincerely thank the reviewer for this insightful and comprehensive suggestion. The manuscript has been substantially expanded to provide Pakistan-specific details as requested: The section “Pakistan’s National PPR Control Programme” now includes a full explanation of the Progressive Control Pathway (Stage 2 – Risk Reduction), highlighting how risk-based vaccination and quarantine are implemented in high-risk zones (border areas, transhumant routes, and outbreak hotspots). The section “PPR Vaccination Strategies and Progress in Pakistan” has been rewritten to detail the national vaccination strategy, local vaccine production (VRI Lahore, SPVC Tandojam), coverage rates, and research advancements including thermostable and adjuvant-enhanced vaccine formulations. Specific incidence trends and the estimated national seroprevalence have been incorporated based on recent field and FAO–WOAH reports. Discussion of control zones, risk mapping, and movement control measures has been elaborated.
Similarly, in Section 9, I suggest that the author elaborate on the content rather than simply listing points	Thank you for this valuable observation. Section 9, previously titled “Thermostable Formulations,” has been completely rewritten to include detailed explanations, examples, and references rather than a list format. The revised section now discusses the principles of vaccine thermostabilization, stabilizing agents (trehalose, gelatin, mannitol), and field relevance to Pakistan’s semi-arid environment.