The severity of COVID-19 compared to seasonal influenza

In a recent study under review at the Archives of Virology journal and currently posted to the Research Square* preprint server, investigators in Israel assessed the disparities and similarities between seasonal influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.

Study: SARS-CoV-2 and Seasonal Influenza: Similarity and Disparity. Image Credit: Lightspring / ShutterstockStudy: SARS-CoV-2 and Seasonal Influenza: Similarity and Disparity. Image Credit: Lightspring / Shutterstock


The coronavirus disease 2019 (COVID-19) combines radiological and clinical features with influenza virus-induced respiratory illness. Unfortunately, it is tough to determine the difference between these two viruses just by examining their clinical presentations. 

Since the start of the SARS-CoV-2 pandemic, researchers have drawn parallels between influenza and COVID-19. The severity of COVID-19 relative to seasonal influenza is still a topic of debate. 

Further, an early distinction between SARS-CoV-2 infection and influenza viruses is critical among hospitalized patients. This is especially crucial at the moment because healthcare institutions are coping with seasonal influenza and the ongoing COVID-19 pandemic. 

Moreover, the epidemiologic implications, the possibility for airborne transmission, inadequate baseline herd immunity, and differing therapeutic methods emphasize the importance of distinguishing between SARS-CoV-2- and influenza-infected patients.

About the study

In the present retrospective research, the scientists determined if there were any variations in clinical presentation and disease severity between influenza and COVID-19 across hospitalized patients. The study was carried out at a 1000-bedded university-affiliated tertiary care hospital treating over two million people in northern Israel, named Rambam Health Care Campus (RHCC). 

The investigation included all adults hospitalized in RHCC with confirmed-COVID-19 during the second SARS-CoV-2 wave in Israel between 1 June 2020 and 31 August 2020. These patients were compared to individuals admitted with influenza-induced respiratory illness between 1 November 2019 and 31 August 2020. The outcomes and clinical features of the hospitalized COVID-19 and influenza patients were compared.

Data including clinical and demographic details, laboratory measures during admission, and the National Early Warning Score 2 (NEWS2), were collected from the RHCC's electronic medical records. Further, the statistical package for social sciences (SPSS) version 26 software was used to analyze the data.

Results and discussions

Collectively, the study results depicted that a total of 152 COVID-19 and 136 influenza patients were included in the study. 

Runny nose, cough, dyspnea, myalgia, and comorbidities were more common in influenza patients than in SARS-CoV-2 patients. Hypoxemia on admission, heightened liver enzymes, or smoking habit was also more prevalent in influenza patients. Overall, the individuals with influenza infection demonstrated typical flu-like symptoms.

Patients with COVID-19, on the other hand, were overweight, had lymphopenia of less than 1500, C reactive protein (CRP) of more than 5 mg/dL, or radiographic anomalies. According to the mounting evidence, chronic inflammation, and excess adiposity associated with obesity enhances the vulnerability to viral infections and illness severity because of immune system dysregulation and high proinflammatory cytokines levels.

The most prevalent laboratory abnormality in COVID-19 patients was lymphopenia, which was 54 times more frequent than in individuals infected with influenza. Direct lymphocytes viral infection due to the presence of angiotensin-converting enzyme 2 (ACE2) receptors on their cell membrane and provoked lymphocyte deficit owing to proinflammatory cytokines were two possibilities that justify the significant lymphopenia in SARS-CoV-2 infection.

COVID-19 patients had a higher percentage of abnormal chest x-rays (CXRs), primarily manifested as bilateral infiltrates. This inference was in line with several earlier studies. However, it was at odds with a prior smaller study. 

Besides, the incidence of dehydration at hospital admission was elevated in SARS-CoV-2 patients. The intravascular exhaustion caused by the virus's direct impact on renal ACE2 receptors might explain this phenomenon.

The demand for ventilatory support, duration of hospital stay, and 30-day mortality were similar in both groups, despite influenza patients experiencing a severe illness with a NEWS2 of more than six on admission. Contrary to the present study, a prior investigation from Germany discovered that hospitalized COVID-19 patients had heightened in-hospital death and poorer clinical outcomes, such as length of hospital stay and ventilation, acute renal injury, and acute respiratory distress syndrome.


Study findings revealed that influenza patients were more critically ill during their stay in the hospital than patients with SARS-CoV-2. Both cohorts, however, had equal in-hospital death and clinical outcomes. 

Furthermore, the two diseases harbored distinct properties that enable them to be separated from one another during the admission time till laboratory diagnosis. The diverse traits of COVID-19 and influenza facilitate the implementation of appropriate preventative strategies and infection control approaches from the point of hospital arrival.

*Important notice

Preprints with Research Square publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Shanet Susan Alex

Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.


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