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Three reviewers have looked at the revised version and indicated that they are satisfied and have no further critiques.
Great article, thank you.
The revised manuscript is very clearly written and the results are interesting. The referee strongly recommend it for publication.
The referee doesn't have further comments.
The manuscript has been revised appropriately and should be accepted for publication.
Two of the reviews contain detailed suggestions that should be helpful to you in revising the manuscript. As you are aware, PeerJ does not place great emphasis on novelty in making publication decisions, but you may wish to clarify the novel contributions of your work to enhance its value to readers as suggested by Reviewer # 3.
Figure 5 : The scale of the incidence is not shown
Line 142 : In general program vaccination target children from 9 to 11 month.
Figure 7 and figure 8 show the intervals between epidemics. These are very interesting findings, though the model assumes no exogenous occurrence of infection. An exogenous infection is a likely event. Either this should be noted in the limitation, or exogenous infection should be integrated in the model.
Line 208-221 :
Seroconversion following vaccination is better in children older than 12 month than in children from 9 to 12 months (from 80% to 95%). The better effectiveness of catch up campaigns might be due to the higher mean age of children vaccinated. Assuming that the better effectiveness of catch campaign is due to better coverage and a better cold chain is a debatable assumption. Indeed, during vaccination campaign, the short duration of the campaign can make difficult for families to vaccinate their children. Moreover, the management of a massive cold chain poses logistic challenges that are not always properly solved. Program vaccination needs a smaller cold chain and offer a longer period to families to bring their children for vaccination. In response to the lower seroconversion rate in young child, A 2 doses vaccination is often recommended in program vaccinations. Usually catch up vaccination target children from 6 or from 9 month. Therefore I don’t think it is wise to recommend a catch up campaign that exclude children younger than 24 months.
I agree that the qualitative fit of the model to the data shows that the model can make the assumption that Beta does not vary by age. However, I don’t find relevant to explain it by the “structure of the African rural Societies” (or give references).
Line 263 :
Could you explain why seasonal forcing is not relevant in Burundi
The article is interesting and clear.
I agree with the main recommendation, however I suggest to model a catch up campaign targeting children from 9 month old.
I think it would be interesting in the future to apply this model in settings that faced measles epidemics every 4 years (like Democratic Republic of Congo).
This paper analyzes a post-honeymoon measles outbreak in the 1989-1999 Muyinga sector (Burundi) by using a partial differential equation epidemic model. The results suggest campaigns should be used regularly to supplement program vaccination. The manuscript is well written, and the result seems interesting. I would like to recommend it for publication in PeerJ.
The following are my suggestions.
1. On Page 3: explain the model formulation.
2. Line 82: is there a boundary condition on right when a=omega (where omega is the oldest age)?
Overall, the paper was well written. It is at the same time concise and complete in thought. There are minor edits that should to made to improve understanding, but not critical to the understanding of the writing overall.
The introduction and background are complete, relevant, and build a complete story for the purpose of this study. The references and background information demonstrate in-depth literature research, and sources cited were an appropriate mix of historical and recent publications. Overall it is well referenced.
The structure conforms to that of PeerJ standards, and raw data and code are supplied.
Figures are relevant and of high quality. Figure descriptions need more information regarding to what certain axes are referring. This particularly pertains to figures 5-7. After fully reading the manuscript, I am assuming that ‘time’ refers to time since vaccination introduction, though it’s not clear. Figures should be essentially stand-alone, so these descriptions should be improved.
In the field of vaccine-preventable diseases, the standard phrasing for vaccination types is “routine vaccination” and “supplemental immunization activities” aka “SIA”. I would recommend revising the manuscript to use this terminology.
The experimental design of the manuscript is original and appropriate. While the concept and model are not novel, their application is. Similarly, while the research question is not novel, and the conclusions to this question, that of the need for vaccination campaigns and broad age ranges of these campaigns are widely accepted, the exact interval of these campaigns and specific age ranges are unique findings. I would recommend explicitly stating this as a primary goal of this study.
The methods are described in sufficient detail for both understanding and replication. The model and relevant equations appear to be valid. Evidence for particular parameter or model decisions are well documented and referenced. Sensitivity analysis, though not explicitly stated, were performed with sufficient consideration and scientific rigor.
The conduct of this study appears to be scientifically and ethically sound.
The data used are robust and statistically sound. The majority of data are from publicly available sources, and that which are not are provided. However, these provided data (measles and chicken pox incidence) are in a format that is not easily understood, and should be resubmitted in a standard format with columns for year/month and incidence.
A major finding of this study is the impact of vaccination on increasing the average age of infection. While this is already a widely accepted occurrence, this study adds important experimental evidence and quantification of this phenomenon. A second major finding is that of the need for either more frequent campaigns or broader age range to prevent post-honeymoon outbreaks. This again is already a widely held concept, yet this study provides beneficial quantitative demonstration of this occurrence and estimates of the age range/campaign interval trade off.
As these are neither novel overall findings nor recommendations, revision is warranted to better demonstrate how these particular findings are important. The policy recommendations from the WHO and other sources are already that vaccination campaigns are necessary in countries with sub-optimal vaccination coverage. Furthermore, given that this study pertains to data from the 1980’s these findings and not directly of value to Burundi. However, the great value of this work is the demonstration, quantitatively, of these phenomena and the estimation of the necessary age ranges and timing intervals campaigns. These should be focused on more.
Overall, this is a well conducted study that provides important evidence to support and quantify occurrences that challenge the current efforts to control and eliminate measles and other vaccine-preventable diseases. This manuscript is generally well written, the science is sound, and it merits publication.
I would like to see some edits prior to publication. These are as follows:
1. Revise the first and second paragraph of the Discussion. The first paragraph needs to immediately restate the purpose or question of the study, and then what this study’s findings contribute. As it is written, I found myself searching for conclusions relevant to the findings, only to be inundated with more citations and irrelevant information (lines 227-231, sentence starting with “One of the insights…” through end of the paragraph are not immediately relevant the findings of this study so should be either moved or deleted).
2. Increase the focus of the discussion and other parts of the paper on the estimation of necessary campaign age ranges and timing intervals.
3. Change terminology to use “routine vaccination” and “supplemental immunization activity” or “SIA”.
- Line 11-12: Restate in the active voice.
- Line 12: Delete comma after ‘vaccination’
- Line 34-37 (“An outbreak of …”): Does not seem relevant or needs to be rephrased.
- Line 46 - “such as ours”: Change to “like ours”. This model has not influenced policy yet.
- Line 72 - “Moreover, the life table…”: While the life table does include deaths, which includes measles deaths, I assume (based on your model above) that you attribute the same death rate to all compartments of the model, so you are actually attributing a slightly reduced death rate to those in the c or z compartments, and slightly increased rate to the other compartments. Probably best here to just delete this sentence.
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