Naming the coronavirus disease and the virus that causes it; Technical guidance; World Health Organization; Available online at: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/technical-guidance/naming-the-coronavirus-disease-(covid-2019)-and-the-virus-that-causes-it (Accessed November 25, 2023).

Sim, M. R. The COVID-19 pandemic: major risks to healthcare and other workers on the front line. Occup. Env. Med. 77, 281–282 (2020).

Article  Google Scholar 

Zhou, P. et al. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature. 579, 270–273 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Ren, L. L. et al. Identification of a novel coronavirus causing severe pneumonia in human: a descriptive study. Chin. Med. J. 133, 1015–1024 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Hosseiny, M., Kooraki, S., Gholamrezanezhad, A., Reddy, S. & Myers, L. Radiology perspective of coronavirus disease 2019 (COVID-19): lessons from severe acute respiratory syndrome and middle east respiratory syndrome. AJR Am. J. Roentgenol. 214, 1078–1082 (2020).

Article  PubMed  Google Scholar 

Venkatram, S., Alapati, A., Dileep, A. & Diaz-Fuentes, G. Change in patterns of hospitalization for influenza during COVID-19 surges. Influenza Other Respir. Viruses 16, 72–78 (2022).

Article  CAS  PubMed  Google Scholar 

Tan, M. P. et al. Dearth of influenza among older adults admitted with respiratory symptoms in Malaysia during the coronavirus disease 2019 pandemic in 2021. Front. Med. 9, 977614 (2022).

Article  Google Scholar 

World Health Organization. Influenza (Seasonal). Available online: https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal) (Accessed November 25, 2023).

Bekkat-Berkani, R. & Romano-Mazzotti, L. Understanding the unique characteristics of seasonal influenza illness to improve vaccine uptake in the US. Vaccine. 36, 7276–7285 (2018).

Article  PubMed  Google Scholar 

Picheta, R., Cotovio, V. & Darlington, S. As hospitals in Brazil teeter on the brink of collapse, Bolsonaro does pushups with supporters. CNN;May 18, 2020. Available online at: https://edition.cnn.com/2020/05/18/americas/brazil-coronavirus-sao-paulo-bolsonaro-rally-intl/index.html (Accessed November 25, 2023).

Olsen, S. J. et al. Decreased influenza activity during the COVID-19 pandemic-United States, Australia, Chile, and South Africa, 2020. Am. J. Transplant. 20, 3681–3685 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Wu, X. J. et al. Co‐infection with SARS‐CoV‐2 and influenza A virus in patient with pneumonia, China. Emerg. Infect. Dis. 26, 1324–1326 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Chen, J., Wang, R., Gilby, N. B. & Wei, G. W. Omicron variant (B.1.1.529): infectivity, vaccine breakthrough, and antibody resistance. J. Chem. Inf. Model. 62, 412–422 (2022).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Radhakrishnan, N. et al. Comparison of the clinical characteristics of SARS-CoV-2 Delta (B.1.617.2) and Omicron (B.1.1.529) infected patients from a single hospitalist service. BMC Infect. Dis. 23, 747 (2023).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Pingping, Z. et al. Comparison between original SARS-CoV-2 strain and omicron variant on thin-section chest CT imaging of COVID-19 pneumonia. Radiologie 63, 55–63 (2023).

Article  PubMed  Google Scholar 

Yang, N. et al. Clinical and pulmonary CT characteristics of patients infected with the SARS-CoV-2 omicron variant compared with those of patients infected with the alpha viral strain. Front. Public. Health. 10, 931480 (2022).

Article  PubMed  PubMed Central  Google Scholar 

HKUMed Finds Omicron SARS-CoV-2 Can Infect Faster and Better Than Delta in Human Bronchus but With Less Severe Infection in Lung. Available online at: https://www.med.hku.hk/en/news/press/20211215-omicron-SARS-CoV-2-infection (Access January 11, 2025).

Wan, X., Wang, W., Liu, J. & Tong, T. Estimating the sample mean and standard deviation from the sample size, median, range and/or interquartile range. BMC Med. Res. Methodol. 14, 135 (2014).

Article  PubMed  PubMed Central  Google Scholar 

Cochrane Handbook for Systematic Reviews of Interventions. Available online at: https://training.cochrane.org/handbook (Access January 11, 2025).

Wallemacq, S. et al. A comparative analysis of the outcomes of patients with influenza or COVID-19 in a tertiary hospital in Belgium. J. Infect. Chemother. 28, 1489–1493 (2022).

Article  PubMed  PubMed Central  Google Scholar 

Mizera, L. et al. COVID-19 versus seasonal influenza: myocardial injury and prognostic importance. BMC Infect. Dis. 22, 539 (2022).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Kim, S. H., Wi, Y. M., Lim, S., Han, K. T. & Bae, I. G. Differences in clinical characteristics and chest images between coronavirus disease 2019 and influenza-associated pneumonia. Diagnostics 11, 261 (2021).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Kronibus, N. et al. Respiratory physiology of COVID-19 and influenza associated acute respiratory distress syndrome. J. Clin. Med. 11, 6237 (2022).

Article  PubMed  PubMed Central  Google Scholar 

Seligman, B. et al. 30-day mortality following COVID-19 and influenza hospitalization among US veterans aged 65 and older. J. Am. Geriatr. Soc. 70, 2542–2551 (2022).

Article  PubMed  Google Scholar 

Kaye, A. D. et al. Economic impact of COVID-19 pandemic on healthcare facilities and systems: In-ternational perspectives. Best. Pract. Res. Clin. Anaesthesiol. 35, 293–306 (2021).

Article  PubMed  Google Scholar 

Hamming, I. et al. Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis. J. Pathol. 203, 631–637 (2004).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Lukassen, S. et al. SARS-CoV-2 receptor ACE2 and TMPRSS2 are primarily expressed in bronchial transient secretory cells. EMBO J. 39, e105114 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Osman, M., Klopfenstein, T., Belfeki, N., Gendrin, V. & Zayet, S. A comparative systematic review of COVID-19 and influenza. Viruses. 13, 452 (2021).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Qu, J. et al. Clinical characteristics of COVID-19 and its comparison with influenza pneumonia. Acta Clin. Belg. 75, 348–356 (2020).

Article  PubMed  Google Scholar 

Ho, F. K. et al. Modifiable and non-modifiable risk factors for COVID-19, and comparison to risk factors for influenza and pneumonia: results from a UK Biobank prospective cohort study. BMJ Open. 10, e040402 (2020).

Article  PubMed  PubMed Central  Google Scholar 

Cai, H. Sex difference and smoking predisposition in patients with COVID-19. Lancet Respir. Med. 8, e20 (2020).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Gonzalez-Rubio, J. et al. A systematic review and meta-analysis of hospitalised current smokers and COVID-19. Int. J. Env. Res. Public. Health 17, 7394 (2020).

Article  CAS  Google Scholar 

Farsalinos, K., Barbouni, A. & Niaura, R. Systematic review of the prevalence of current smoking among hospitalized COVID-19 patients in China: could nicotine be a therapeutic option? Intern. Emerg. Med. 15, 845–852 (2020).

Article  PubMed  PubMed Central  Google Scholar 

Piao, W. H. et al. Nicotine and inflammatory neurological disorders. Acta Pharmacol. Sin. 30, 715–722 (2009).

Article  CAS  PubMed  PubMed Central  Google Scholar 

Faust, J. S. & Rio, C. D. Assessment of deaths from COVID-19 and from seasonal influenza. JAMA Intern. Med. 180, 1045–1046 (2020).