Dear Dr Thompson,

Thank you very much for submitting your manuscript "Prioritising older individuals for COVID-19 booster vaccination leads to optimal public health outcomes in a range of socio-economic settings" for consideration at PLOS Computational Biology. As with all papers reviewed by the journal, your manuscript was reviewed by members of the editorial board and by several independent reviewers. The reviewers appreciated the attention to an important topic. Based on the reviews, we are likely to accept this manuscript for publication, providing that you modify the manuscript according to the review recommendations.

Please prepare and submit your revised manuscript within 30 days. If you anticipate any delay, please let us know the expected resubmission date by replying to this email.

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[1] A letter containing a detailed list of your responses to all review comments, and a description of the changes you have made in the manuscript. Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out

[2] Two versions of the revised manuscript: one with either highlights or tracked changes denoting where the text has been changed; the other a clean version (uploaded as the manuscript file).

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Thank you again for your submission to our journal. We hope that our editorial process has been constructive so far, and we welcome your feedback at any time. Please don't hesitate to contact us if you have any questions or comments.

Sincerely,

Claudio José Struchiner, M.D., Sc.D.

Academic Editor

PLOS Computational Biology

Thomas Leitner

Section Editor

PLOS Computational Biology

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Reviewer's Responses to Questions

Comments to the Authors:

Please note here if the review is uploaded as an attachment.

Reviewer #1: The available vaccinations against SARS-CoV-2 protect against severe courses and death from the coronavirus, both on an individual and societal level. However, this protection is not permanent and therefore booster vaccinations are required.

The authors address the important question of which age groups should have access to booster vaccination and in what order to achieve an optimal effect. They consider different scenarios in several countries with the help of a mathematical model.

The methods used are appropriate, rigorous and detailed. The results are novel, relevant, and convincing. The discussion is comprehensive, fair, and balanced.

In approximately 20 years as a reviewer, this is the first time I have recommended accepting a manuscript in its original form. I would like to congratulate the authors on their excellent work.

Reviewer #2: It has been a pleasure to review the manuscript "Prioritising older individiuals for COVID-19-booster vaccination leads to optimal public health outcomes in a range of socio-economic settings".

The authors present a computational study of the outcomes (e.g. years of life lost) of different booster vaccination strategies (in terms of what population groups are prioritised), and apply the the approach to different socio-economic settings (from high to low income countries).

The underlying mathematical model is a deterministic, compartmental model of SEIR-type, with a chain of E compartments to model Gamma-distributed exposed times, and age-structure. It is a well-established and well-justified model of COVID-19.

Some of the parameter assumptions are quite strong. For example, assuming that the core infection parameter values are the same in all countries. However, the authors allowed for uncertainty in the parameters, and the results are robust to the uncertainty. However, it is not easy for the reader to discern what parameters are fixed and what parameters include uncertainty. Similarly, and although the robustness of the results is without question, the details on how some of the parameter models are fitted are not included in the manuscript.

Overall, this is an excellent study, and my comments below are just minor suggestions to improve the readibilty of the article.

Minor suggestions:

- Include confidence intervals in panel A of figures 4 and 5, even if they are small at that scale. Although the uncertainty is clear from panel B, it will help understand the robustness of the results.

- Describe clearly what parameters are taken as fixed, and what parameters include uncertainty.

- Describe the details of the MCMC estimates, even if it just in the supplementary material (for example, how many samples were generated, how was convergence assessed).

- In the supplementary material, Fig S1 suggests that in certain socio-economics settings (e.g. lower income countries), there are no significant differences between several strategies when the assumptions are relaxed (or alternatively, when more uncertainty is allowed in the assumptions). The overall conclusion of the paper in favour of Strategy 1 remains the same, but Fig S1 suggests than in certain settings the policy-makers can take a range of decisions about the strategy without affecting the final outcomes. Please consider including that observation in the main text.

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: No

Reviewer #2: No

Figure Files:

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References:

Review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript.

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Dear Dr Thompson,

We are pleased to inform you that your manuscript 'Prioritising older individuals for COVID-19 booster vaccination leads to optimal public health outcomes in a range of socio-economic settings' has been provisionally accepted for publication in PLOS Computational Biology.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. A member of our team will be in touch with a set of requests.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

Should you, your institution's press office or the journal office choose to press release your paper, you will automatically be opted out of early publication. We ask that you notify us now if you or your institution is planning to press release the article. All press must be co-ordinated with PLOS.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Computational Biology. 

Best regards,

Claudio José Struchiner, M.D., Sc.D.

Academic Editor

PLOS Computational Biology

Thomas Leitner

Section Editor

PLOS Computational Biology

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