Comparison of the Characteristics of Patients Admitted to the Intensive Care Unit During Peak Periods of SARS-CoV-2 Variants

Can Ömür^1*, Hüseyin Arıkan¹, Sait Karakurt¹

¹Department of Pulmonology and Intensive Care, Marmara University School of Medicine, Pendik, 34899, Istanbul, Türkiye

*Correspondence author: Can Ömür, MD, Department of Pulmonology and Intensive Care, Marmara University School of Medicine, Pendik, 34899, Istanbul, Türkiye; Email: caan.mr@gmail.com

Citation: Ömür C, et al. Comparison of the Characteristics of Patients Admitted to the Intensive Care Unit During Peak Periods of SARS-CoV-2 Variants. Jour Clin Med Res. 2025;6(3):1-9.

Copyright^© 2025 by Ömür C, et al. All rights reserved. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Table 1: Demographic characteristics of participants.

Table 2: Vaccination and mortality status.

Table 3: Intensive Care Unit (ICU) treatments.

Table 4: Treatments administered in the ICU.

Table 5: Multivariate logistic regression analysis of factors associated with mortality.

Table 6: Post-discharge outcomes and follow-up findings.

Discussion

This single-center retrospective study provides a comparative evaluation of the clinical characteristics, laboratory findings, treatment approaches and mortality rates of patients admitted to the ICU during four waves of the COVID-19 pandemic in Türkiye between November 2020 and March 2022. Our findings highlight several critical observations, including a high median patient age, an increase in comorbidity burden particularly in the third and fourth waves (CCI was highest in the 4^th wave), low vaccination coverage, inter-wave variations in laboratory parameters and a significant rise in mortality rates over time. These data are valuable for understanding changes in patient profiles and clinical burden across different phases of the pandemic and for guiding health system preparedness and resource allocation.

This study encompasses a period marked by rapid evolution of SARS-CoV-2, during which successive variants exerted considerable pressure on global healthcare systems. The Alpha and Beta variants were predominant in the first two waves, the Delta variant in the third and the Omicron variant in the fourth wave [8-10,23]. Our findings demonstrate that even during the Omicron-dominant wave, ICU admissions primarily involved elderly patients with significant comorbidity burdens, emphasizing that high transmissibility of Omicron continued to pose severe risks to vulnerable populations. This partially contrasts with reports suggesting a generally milder course for Omicron infections [9]. The persistence of severe illness in high-risk groups despite variant-specific differences highlights the need to consider population risk distribution in pandemic response strategies. Reports from the United Kingdom and South Africa similarly indicated that while overall hospitalization rates decreased during the Omicron wave, ICU demand persisted in older patients and those with multiple comorbidities [9,21,28].

The median age of 70 years and male predominance (58%) in our cohort align with global data showing that advanced age is strongly associated with severe disease and mortality and that men are disproportionately affected [2,4,15]. HT (55%), DM (36%), CVD (28%) and COPD (15%) were the most common comorbidities. The marked increase in CCI scores observed during the fourth wave suggests that severe disease became increasingly concentrated among frail populations over time. These findings underscore the importance of prioritizing high-risk groups in vaccination programs and implementing individualized protective strategies. Symptom profiles in our study were consistent with the typical clinical presentation of COVID-19, with dyspnea (72%), fever (65%) and cough (59%) being the most frequent. Altered mental status was reported in 12% of patients, potentially reflecting hypoxemia and severe systemic inflammation [15,16,29]. This underscores the multisystemic nature of severe COVID-19. Laboratory findings highlighted elevated ferritin, dand D-dimer levels as prominent markers. Ferritin levels were highest during the 2^nd and 3^rd waves, while LDH peaked in the 1^st and 4^th waves. These results are consistent with previous studies demonstrating the prognostic significance of these biomarkers [4,15]. IMV was required in 46% of patients, increasing to 55% during the fourth wave. HFNO use was particularly high in the 3rd wave (64.2%), whereas NIMV use significantly decreased in the 4^th wave (16.7%). RRT was required in 28.6%. RRT requirement demonstrates the significant contribution of multi-organ failure to disease severity [12,13]. The incidence of secondary infections was 58.4% overall, with the highest rate in the 1^st wave (80.3%), underscoring the risks of prolonged mechanical ventilation and highlighting the importance of stringent infection prevention and multidisciplinary ICU management. Treatment strategies in our study mirrored national and international guidelines [1,11]. Corticosteroids were consistently administered across all waves, becoming a global standard following the RECOVERY trial [18]. The increased use of tocilizumab and remdesivir during the second and third waves reflects evolving clinical evidence and therapeutic availability, demonstrating the adaptability of treatment protocols throughout the pandemic. Low vaccination coverage emerged as a major public health challenge. Seventy-five percent of patients were unvaccinated, a statistic likely influenced by vaccine hesitancy and logistical delays in vaccine distribution. In the 4th wave, patients with at least one vaccination had significantly lower mortality compared with unvaccinated patients (p=0.024). Studies have shown that mRNA and inactivated vaccines significantly reduce the risk of severe disease and death [20-23]. However, their effectiveness in high-risk populations is relatively reduced and booster doses are essential. Our findings reinforce the need for targeted vaccination campaigns and booster strategies for vulnerable populations. The ICU mortality rate in this cohort was 80%, reflecting the severe disease burden during the peak pandemic periods. Mortality increased from 65.6% in the first wave to 84% in the third and 82.5% in the fourth wave. Global reports indicate ICU mortality rates ranging from 40% to 80%, influenced by healthcare infrastructure, ICU capacity, access to therapeutics and national response strategies [12,13,16]. Although Türkiye increased ICU bed capacity during the pandemic, surges in patient volume challenged healthcare resources, demonstrating the need for sustainable surge capacity planning.

Long-term complications of COVID-19 were also notable in this study. Post-discharge, 40% of survivors required supplemental oxygen for up to six months and 15% experienced long COVID symptoms (e.g., fatigue, dyspnea). These results align with studies reporting persistent respiratory impairment and reduced quality of life in 30-50% of severe COVID-19 survivors [29,30]. This highlights the ongoing burden of COVID-19 beyond the acute phase and the necessity of multidisciplinary rehabilitation programs, long COVID clinics and structured follow-up care. Post-COVID psychiatric morbidity and socioeconomic impacts should also be prioritized in health policy planning.

Key strengths of this study include the large ICU patient cohort, standardized management protocols and comparative analysis across four pandemic waves. The single-center design enhanced data consistency and the retrospective approach allowed for rapid data collection. However, limitations include reliance on epidemiological rather than genomic data for variant classification and reduced generalizability due to the single-center setting. Despite these limitations, this study provides rare and detailed insights into the changing clinical burden and patient profile of ICU admissions across different variant-dominant periods in Türkiye.

Conclusion

This study demonstrates that even during later stages of the pandemic, ICU admissions primarily involved elderly patients with multiple comorbidities and mortality remained high. These findings emphasize the need for targeted protection of high-risk populations, widespread administration of booster doses and ongoing investment in ICU capacity. Multidisciplinary care approaches, early access to treatment and robust public health interventions remain critical to pandemic response. The results presented here offer a strategic roadmap for preparedness against future pandemics and highlight the necessity of prioritizing long COVID management within healthcare systems.

Conflict of Interest

Authors have no conflicts of interest to disclose / disclose any relationships or activities.

Funding

This study was funded by the author, and no additional grants were received.

Acknowledgment

The author thanks the clinical team and the patient for their cooperation.

Disclaimer

The views expressed in this manuscript are solely those of the authors and do not necessarily represent the official policy or position of their respective institutions.

Data Availability Statemen

The data that support the findings of this study are available to the corresponding author upon reasonable request.

Disclosure of Relationships and Activities

Authors have no conflicts of interest to disclose / disclose any relationships or activities.

Author’s Contribution

Conceptualization: Can Ömür, Hüseyin Arıkan. Study Design: Can Ömür, Hüseyin Arıkan. Data Collection and Processing: Can Ömür, Hüseyin Arıkan. Data Analysis and Interpretation: Can Ömür, Hüseyin Arıkan. Supervision: Sait Karakurt. Writing – Original Draft: Can Ömür. Writing – Review and Editing: Hüseyin Arıkan, Sait Karakurt. Validation: Hüseyin Arıkan. Visualization: Can Ömür. Project Administration: Sait Karakurt.

All authors contributed to the writing and have approved the final version of the manuscript.

References

1. 2020 World Health Organization. WHO Director-General’s opening remarks at the media briefing on COVID-19. 2020. Geneva: World Health Organization. 2020. [Last Accessed on: October 20, 2025]

https://www.who.int/news-room/detail/11-03-2020

2. Zhu N, Zhang D, Wang W. A Novel coronavirus from patients with pneumonia in China, 2019. N Engl J Med. 2020;382:727-733.
3. Faria NR, Mellan TA, Whittaker C. Genomics and epidemiology of the P.1 SARS-CoV-2 lineage in Manaus, Brazil. Science 2021;372:815-21.
4. Wang D, Hu B, Hu C. Clinical characteristics of 138 Hospitalized Patients With 2019 novel coronavirus-infected pneumonia in Wuhan, China. JAMA. 2020;323:1061-9.
5. Davies NG, Abbott S, Barnard RC. Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England. Science. 2021;372.
6. Korber B, Fischer WM, Gnanakaran S. Tracking changes in SARS-CoV-2 spike: Evidence that D614G increases infectivity of the COVID-19 virus. Cell. 2020;182:812-27.
7. Lu R, Zhao X, Li J. Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. Lancet 2020;395:565-574.
8. 2023 World Health Organization. Tracking SARS-CoV-2 variants. Geneva: WHO. 2023. [Last Accessed on: October 20, 2025] https://www.who.int/activities/tracking-SARS-CoV-2-variants
9. Karim SSA, Karim QA. Omicron SARS-CoV-2 variant: a new chapter in the COVID-19 pandemic. Lancet 2021;398:2126-8.
10. Ministry of Health – Republic of Turkey. [Last Accessed on: October 20, 2025]

https://covid19.saglik.gov.tr/

11. 2020 Republic of Turkey Ministry of Health. COVID-19 Guidelines. [Last Accessed on: October 20, 2025]

https://covid19.saglik.gov.tr/TR-66301/COVID-19-rehberi.html

12. Auld SC, Caridi-Scheible M, Blum JM. ICU and ventilator mortality among critically Ill adults with coronavirus disease 2019. Crit Care Med. 2020;48:e799-804.
13. Grasselli G, Greco M, Zanella A. Risk factors associated with mortality among patients with COVID-19 in intensive care units in Lombardy, Italy. JAMA Intern Med 2020;180:1345-55.
14. Huang C, Wang Y, Li X. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 2020;395:497-506.
15. Wu Z, McGoogan JM. Characteristics of and important lessons from the Coronavirus Disease 2019 (COVID-19) outbreak in China: Summary of a report of 72 314 cases from the chinese center for disease control and prevention. JAMA. 2020;323:1239-42.
16. Challen R, Brooks-Pollock E, Read JM, Dyson L, Tsaneva-Atanasova K, Danon L. Risk of mortality in patients infected with SARS-CoV-2 variant of concern 202012/1: Matched cohort study. BMJ. 2021;372:n579.
17. Beigel JH, Tomashek KM, Dodd LE. Remdesivir for the treatment of COVID-19 – final report. N Engl J Med. 2020;383:1813-26.
18. Horby P, Lim WS, Emberson JR. Dexamethasone in Hospitalized Patients with COVID-19. N Engl J Med. 2021;384:693-704.
19. Kalil AC, Patterson TF, Mehta AK. Baricitinib plus remdesivir for hospitalized adults with COVID-19. N Engl J Med 2021;384:795-807.
20. Variation in the COVID-19 infection-fatality ratio by age, time and geography during the pre-vaccine era: a systematic analysis. Lancet 2022;399:1469-88.
21. Feikin DR, Higdon MM, Abu-Raddad LJ. Duration of effectiveness of vaccines against SARS-CoV-2 infection and COVID-19 disease: results of a systematic review and meta-regression. Lancet. 2022;399:924-44.
22. Voysey M, Clemens SAC, Madhi SA. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: An interim analysis of four randomised controlled trials in Brazil, South Africa and the UK. Lancet. 2021;397:99-111.
23. Nordström P, Ballin M, Nordström A. Risk of infection, hospitalisation and death up to 9 months after a second dose of COVID-19 vaccine: A retrospective, total population cohort study in Sweden. Lancet. 2022;399:814-23.
24. Prokop M, van Everdingen W, van Rees Vellinga T. CO-RADS: A categorical CT assessment scheme for patients suspected of having COVID-19-definition and evaluation. Radiology. 2020;296:E97-104.
25. Vincent JL, Moreno R, Takala J. The SOFA (Sepsis-related Organ Failure Assessment) score to describe organ dysfunction/failure. On behalf of the working group on sepsis-related problems of the european society of intensive care medicine. Intensive Care Med. 1996;22:707-10.
26. Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: A severity of disease classification system. Crit Care Med 1985;13:818-29.
27. Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chronic Dis. 1987;40:373-83.
28. Tegally H, Wilkinson E, Giovanetti M. Detection of a SARS-CoV-2 variant of concern in South Africa. Nature. 2021;592:438-43.
29. Magesh S, John D, Li WT. Disparities in COVID-19 outcomes by race, ethnicity and socioeconomic status: A systematic-review and meta-analysis. JAMA Netw Open. 2021;4:e2134147.
30. Nalbandian A, Sehgal K, Gupta A. Post-acute COVID-19 syndrome. Nat Med. 2021;27:601-15.