Dear Dr. Didriksson,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please address the minor changes suggested by the rviewers

Please submit your revised manuscript by Jan 08 2026 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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We look forward to receiving your revised manuscript.

Kind regards,

Andrea Martinuzzi

Academic Editor

PLOS ONE

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7. Please 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 If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references.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. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Partly

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: The background (“The understanding of recovery after critical COVID-19 beyond the first year is limited”) is too generic (L27–29). It should briefly reference existing one- or two-year follow-up gaps in research to frame the novelty more clearly — e.g., “Few studies extend beyond 24 months, and long-term trajectories remain poorly defined.”

The citations are comprehensive but descriptive. The authors could improve critical engagement by distinguishing methodological limitations of prior studies (e.g., smaller sample sizes, lack of frailty stratification, non-longitudinal design). For example, line 72–79 could add: “However, most studies employed self-reported symptom tracking rather than structured clinical scales, limiting comparability over time.”

The narrative shifts abruptly from COVID-19 sequelae (L58–64) to ARDS comparators (L63–67). The transition sentence could better explain why comparing COVID-19 with ARDS survivors is justified — e.g., shared pathophysiology or recovery trajectories.

Frailty and comorbidity are both considered, but their measurement overlap is not addressed. The Charlson Comorbidity Index or equivalent could have provided a more granular control for chronic disease confounding. Moreover, ICU treatment variables (ventilation duration, sedation depth, corticosteroid use) are not modeled, though they can strongly affect long-term outcomes.

Improvement: Include these as covariates or discuss them as unmeasured confounders.

Reviewer #2: I thank the Editor for the opportunity to review the manuscript “Three-year functional, physical, and mental health outcomes after critical COVID-19: A prospective multicentre cohort study” by Dr Didriksson and colleagues. In the manuscript the authors report results from a follow-up telephone assessment of patients that have survived critical COVID-19 three years previously, and compare the results with previous assessments of the same cohort. The results are interesting, and the authors should be commended for the focus on patient-important outcomes and good retention of the cohort. The main result was that at three years, the patients´ functional outcome had impaired compared to the one-year follow-up. This is unsettling, as especially younger age, but also frailty, appears as a risk factor for deterioration. The study has several merits, such as use of validated instruments by trained assessors, and a small number of dropouts. The manuscript is well written, easy to follow, and the figures and tables are clear. I have, however, some questions regarding the study and interpretation of the results that need clarification.

1. The one-year mortality in the original cohort seems very high (48%), when compared with the 30-d mortality of 27% in Sweden, reported in a study by Chew et al [1]. Can the authors discuss this and how a potentially higher than average mortality and probably disease severity, affect the generalizability of the results?

2. Although the retention was good, almost 10% of the patients dropped out between 1- and 3-year follow-ups. Did the authors assess who these drop-outs were?

3. There was a considerable number of non-native Swedish speaking patients in the cohort, how does this affect the results? Do the population norms fit well for immigrants? Are there cultural or language-related aspects in interpreting the results of the questionnaires? Do the population norms fit well in analysing results in immigrant populations?

4. How would the different assessment methods, face-to-face and telephone assessment affect the results? The authors have listed this as a limitation, but since the result of impairment in the results is not unsurprising, it would be valuable to discuss the differences in more detail.

5. One important issue is that there are no controls in this study. Pandemic affected the whole society in most countries in many different ways, which may compromise population norms as a standard, because also individuals without critical covid or no covid at all may have experienced challenges in mental health. Mirroring the results of this cohort to contemporary controls might have given different, less dramatic impairment. Please discuss. I am aware that a control group with no COVID-19 at all would be almost impossible to obtain, but the challenges of a design with no controls should be acknowledged.

6. In intensive care literature on long-term follow-up there is an inherent challenge that the connection to the initial event (here COVID-19) becomes weaker as time passes, and other life events occur and confound the results. In this study, too, it is possible that the patients experience life events that are not at all related to the COVID-19. Also here, the control group would be helpful. It would be important to discuss also this aspect, that it is not clear how much these results are due to history of covid, or are they possibly a result of other challenges, such as aging, other diagnoses, etc.

7. Did the authors record any psychiatric diagnoses at baseline? This would be important information for interpreting the results.

8. Some of the patients were still receiving rehabilitation at three years. How were patients supported if they were found having psychiatric symptoms at one-year follow-up? Did they receive support, and could this have affected the results?

Ref.

1. Chew MS, Kattainen S, Haase N, Buanes EA, Kristinsdottir LB, Hofsø K, Laake JH, Kvåle R, Hästbacka J, Reinikainen M, Bendel S, Varpula T, Walther S, Perner A, Flaatten HK, Sigurdsson MI. A descriptive study of the surge response and outcomes of ICU patients with COVID-19 during first wave in Nordic countries. Acta Anaesthesiol Scand. 2022 Jan;66(1):56-64. doi: 10.1111/aas.13983. Epub 2021 Oct 3. PMID: 34570897; PMCID: PMC8652908.

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what does this mean? ). If published, this will include your full peer review and any attached files.

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Reviewer #1: No

Reviewer #2: No

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Attachments

Attachment

Submitted filename: PONE review.pdf

Dear Dr. Didriksson,

• The manuscript is much improved and now requires only minor adjustments detailed by reviewer 1.

plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

• A letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols .

We look forward to receiving your revised manuscript.

Kind regards,

Andrea Martinuzzi

Academic Editor

PLOS One

Journal Requirements:

1. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise.

2. Please 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. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #1: Partly

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1:  Introduction remains largely descriptive rather than hypothesis-driven. While the gap in knowledge is clearly articulated, the manuscript would benefit from a clearer articulation of expected trajectories between 1 and 3 years. In addition, while the authors cite relevant two-year studies, the Introduction could more clearly differentiate critical COVID-19 survivors from general hospitalized COVID-19 populations in terms of pathophysiology and recovery expectations.

There are several methodological choices deserve deeper discussion. The transition from predominantly face-to-face follow-up at 1 year to exclusively telephone-based follow-up at 3 years introduces a non-trivial risk of measurement drift, particularly for clinician-reported outcomes such as GOSE. Although the authors acknowledge this limitation later, it would strengthen the Methods section to explicitly justify why telephone administration is considered comparable, or to cite validation studies specific to ICU or post-COVID populations.

The absence of a formal sample size calculation is understandable given the population-based design, but the manuscript would benefit from a brief discussion of statistical power, especially for multivariable regression analyses. Readers are left uncertain whether null findings for ICU severity variables reflect true lack of association or limited power.

The regression modeling strategy is sound but constrained. By excluding variables with higher missingness and focusing primarily on baseline characteristics, the multivariable model is structurally predisposed to identify age and frailty while under-representing social, occupational, and rehabilitation-related determinants that may be more relevant at three years.

Results would benefit from a stronger emphasis on heterogeneity. While group-level changes are clear, readers are left without a sense of which subgroups are most affected beyond age and frailty. Stratified analyses—by age group, employment status, or baseline mental health—would add important clinical nuance and help clinicians identify patients at greatest risk.

Reviewer #2: The authors have done a substantial amount of work and the manuscript has improved. They have responded to my questions and comments satisfactorily.

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what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #1: No

Reviewer #2: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

To ensure your figures meet our technical requirements, please review our figure guidelines: https://journals.plos.org/plosone/s/figures

You may also use PLOS’s free figure tool, NAAS, to help you prepare publication quality figures: https://journals.plos.org/plosone/s/figures#loc-tools-for-figure-preparation.

NAAS will assess whether your figures meet our technical requirements by comparing each figure against our figure specifications.

Three-year functional, physical, and mental health outcomes after critical COVID-19: A prospective multicentre cohort study

PONE-D-25-38284R2

Dear Dr. Didriksson,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Andrea Martinuzzi

Academic Editor

PLOS One

Additional Editor Comments (optional):

Reviewers' comments: