A Comparative Analysis Show Distinct Severity of COVID-19 vs Influenza


Results of a study by Yan Xie and colleagues highlight the severe impact of COVID-19, with higher death rates, increased risks of long-term complications, and greater infectivity compared to seasonal influenza.

This article originally appeared on our sister site, Infection Control Today.

A recent article by Yan Xie and colleagues1 presented strong data that COVID-19 is much worse than the seasonal flu.

The researchers observed increased rates of delayed and long-term death and disability in US military veterans who were hospitalized with COVID-19 as compared to those hospitalized with seasonal influenza. The COVID-19 group of patients had a 51% higher chance of death over an 18-month follow-up period. When the researchers analyzed 94 prespecified diseases or disorders, patients who had COVID-19 had an increased risk of acquiring 64 of these adverse outcomes, as patients’ post-influenza had an increased risk for only 6. Except for the pulmonary system, patients with SARS-CoV-2 had an increased risk of developing diseases in various organ systems. SARS-CoV-2 patients also experienced 287 disability-adjusted life years per 100 patients, as those post-influenza experienced 243 disability-adjusted life years per 100 patients.

The Veterans Health Administration services an older population compared to many healthcare systems. But, there are also higher rates of obtaining COVID-19 boosters in older patients,2 which may explain the CDC survey findings that the peak incidence for reporting long-term COVID occurs in ages 30 to 50 years as opposed to those 70 years and older.3

Analyzing CDC reporting system data, the authors also determined that there are 2 to 3 times as many hospitalizations for COVID-19 as for seasonal influenza.

Most importantly, the impact on society is not just determined by the case fatality or disability rate for those infected with a dangerous pathogen. Infectivity is also of utmost importance, especially for SARS-CoV-2, an immunoevasive mutating virus that all too commonly causes reinfections.

From the onset of the epidemic, SARS-CoV-2 was known to be highly infectious. Early research estimated the R0 to be approximately 2.5, as influenza during the 2009 Swine flu pandemic had a R0 of approximately 1.5.4 Other researchers have estimated an R0 for SARS-CoV-2 of 2.63.5 The R0 for seasonal influenza has a mean of approximately 1.3.6 However, as the SARS-CoV-2 pandemic progressed, interventions such as vaccines and masking lowered the effective R0. Later, in 2021 and 2022, the virus became more infective with the Delta and Omicron variants. By 2023, public health interventions were largely ignored in the United States, with little use of facial masks and only 18.3% of adults receiving the XBB booster as of December 8, 2023.2 The shifting nature of the virus and public response has made the effective R0 difficult to calculate.

What You Need to Know

Patients with COVID-19, especially US military veterans, faced higher rates of delayed and long-term death and disability compared to those with seasonal influenza.

The article emphasizes the importance of infectivity, noting that SARS-CoV-2 is highly infectious, with 2.87 times as many new cases and 5 times as many new hospitalizations compared to seasonal influenza.

The article underscores that the impact of a viral outbreak extends beyond case fatality or disability rates.

To estimate comparative infectivity, data was obtained from EPIC’s COSMOS initiative (https://epicresearch.org/data-tracker). EPIC is the largest provider of electronic medical record systems in the United States.

The number of new cases diagnosed each week for influenza and SARS-CoV-2 for weekly starting dates of December 4, 2022, through November 26, 2023, were used for comparison. During this period, there were 2.87 times as many SARS-CoV-2 (5,572,366 cases) as seasonal influenza cases (1,772,602 cases). (EPIC collected ICD-10 data from medical visits and laboratory results from over 220 large health care systems, which report their medical record data to COSMOS.)

The COSMOS data documented 5 times more new hospitalizations with COVID-19 than seasonal influenza. The greater number of COVID-19 hospitalizations reported in the COSMOS data, compared to the CDC data, may be due to less politicization in data collection and greater uniformity in the methodology in capturing cases caused by the 2 pathogens. Hence, one can argue that the findings described by Yan Xie and colleagues may have a much more significant impact on society.

Xie and colleagues’ research also underscores the dangers of influenza, which is minimized by far too many in our society. It should also be remembered that the impact of death from SARS-CoV-2 and long COVID is in addition to, not instead of, cases incurred with influenza.

The high rates of death and disability from SARS-CoV-2, compared to seasonal influenza, along with its increased infectivity, makes slowing viral spread and development of next-generation vaccines imperative.


1. Xie Y, Choi T, Al-Aly Z. Long-term outcomes following hospital admission for COVID-19 versus seasonal influenza: a cohort study. Lancet Infect Dis. 2023.Accessed December 28, 2023. https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(23)00684-9/fulltext

2. Weekly COVID-19 Vaccination Dashboard [Internet]. CDC. 2023 [cited Dec. 4, 2023]. Accessed December 28, 2023. https://www.cdc.gov/vaccines/imz-managers/coverage/covidvaxview/interactive/vaccination-dashboard.html.

3. Long COVID - Household Pulse Survey - COVID-19. CDC. Accessed December 28, 2023. https://www.cdc.gov/nchs/covid19/pulse/long-covid.htm

4. Petersen E, Koopmans M, Go U, Hamer DH, Petrosillo N, Castelli F, et al. Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics. Lancet Infect Dis. 2020;20(9):e238-e44.Accessed December 28, 2023.https://pubmed.ncbi.nlm.nih.gov/32628905/

5. Mahase E. Covid-19: What is the R number? BMJ. 2020;369:m1891.Accessed December 28, 2023. https://www.bmj.com/content/369/bmj.m1891

6. Coburn BJ, Wagner BG, Blower S. Modeling influenza epidemics and pandemics: insights into the future of swine flu (H1N1). BMC Med. 2009;7:30.Accessed December 28, 2023. https://bmcmedicine.biomedcentral.com/articles/10.1186/1741-7015-7-30

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