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COVID-19 Vs Influenza – A Retrospective Look at Patient Outcomes

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COVID-19 Vs Influenza – A Retrospective Look at Patient Outcomes

I want to start by saying that in no way is this article politically motivated or aims to judge how governments have handled the Coronavirus disease 2019 (COVID-19) pandemic. Only time will provide such answers. And when we are telling our children and grandchildren the stories of 2020 – and hopefully not too much of 2021 – we will know whether governments nailed it, or over-reacted. This article was motivated by a study I read comparing patients hospitalised with either COVID-19 or seasonal influenza.

Disclaimer out of the way.

Before the pandemic really took shape, I remember downplaying the situation, likening the severity of COVID-19 with influenza. I was wrong and uninformed. In my defence, I think we all were at that point. The virus spread faster than we could control, culminating in the situation we find ourselves in now. For many, that’s still a lockdown, and for many others, the threat of a viral resurgence resulting in… another lockdown.

With the gravity of the situation now clear, we know that COVID-19 – caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – is a severe disease that has sadly caused over 2 million deaths. However, to compare it to influenza we need some evidence backed up by scientific rigour. And thanks to The Lancet making all their COVID-19 resources free to access, I successfully located a study comparing risk factors, clinical characteristics and outcomes of patients hospitalised for either COVID-19 or influenza.

“Comparison of the characteristics, morbidity, and mortality of COVID-19 and seasonal influenza: a nationwide, population-based retrospective cohort study” written by Peroth et al., used discharge summaries from hospitals in France to retrospectively compare the two groups. Included were:

  • 89,530 patients with COVID-19, hospitalised between 1 March and 30 April, 2020; and
  • 45,819 patients with influenza, hospitalised between 1 December, 2018 and 28 February, 2019 (the 2018/19 influenza season).

Both groups had patients of varying ages and with a mixture of comorbidities.

The results:

  • Twice as many patients were hospitalised for COVID-19 than influenza over a shorter period.
  • COVID-19 patients were more likely to need intensive care, and their average length of stay in intensive care was nearly twice as long.
  • A quarter of COVID-19 patients remained in intensive care for more than three weeks.
  • Patients with COVID-19 were more likely to require mechanical ventilation.
  • The mortality rate for patients with COVID-19 was approximately three times higher compared to patients with influenza.
  • Respiratory problems were more common in patients with COVID-19, and they were more likely to develop acute respiratory failure, pulmonary embolism, septic shock or have a haemorrhagic stroke. However, Influenza patients were more likely to have a heart attack or develop atrial fibrillation.


Now I have cherry-picked the primary results here. And one can extrapolate from the study further results that look at different subgroups – notably weight, age and comorbidities. But the results speak a clear message: there are significant differences in patient outcomes between the two viruses, with SARS-CoV-2 – statistically – causing more serious disease and putting a greater strain on healthcare systems.

I don’t want to delve into the subgroups too much, but I would like to mention the information this study found on paediatric patients. A common conversation I hear about this virus and disease is that, so long as you’re young and healthy, you’re in no danger. Certainly, the risk of SARS-CoV-2 causing serious disease is higher if you are older and have comorbidities – this is widely accepted. But being young does not automatically cross you off the virus’s hit list.

Although the proportion of paediatric patients (<18 years) was smaller for COVID-19 than for influenza (suggesting SARS-CoV-2 generally causes less severe disease in children and they are less likely to require hospitalisation), the in-hospital mortality rate for this group was four-times higher than those with influenza. It must be noted that these results were based on small numbers in the study, and therefore hold less statistical weight. But as the authors of the study suggest, these results imply that SARS-CoV-2 is intrinsically more severe than influenza.

Like any study, there were several limitations, most notably in my opinion, is that it only looked at patients who were hospitalised. It did not examine the greater population infected with either virus that experienced only mild symptoms, therefore not requiring hospitalisation. This, of course, would give us a much clearer picture of which virus causes more severe disease. However, such a study's complexity would be immense, leaving us with the information we have at hand and hoping for more detailed research in the future.

It is worth noting that the 2018/19 influenza season had the highest case-fatality rate in France within the past five years. Thus, the COVID-19 cohort in this study was compared against a severe strain of influenza – further adding to the argument that SARS-CoV-2 is intrinsically more severe. Indeed, with the total number of deaths caused by COVID-19 passing the grim total of 2 million recently, and the average annual number of deaths caused by seasonal influenza estimated between 291,243 and 645,832; the saddening numbers support this claim.

Backing up this study’s findings was another small study out of Finland that posed the same questions. Although only 61 patients were studied – greatly limiting the statistical weight of the findings – the results showed that COVID-19 patients were more likely to need intensive care treatment, and for longer periods; were hospitalised longer and the disease was more likely to progress in severity.

Our knowledge of SARS-CoV-2 is juvenile. Scientists have had insufficient time to study it like we have influenza or other common viruses. It exploded out of Wuhan, China and strangled populations and economies around the world. But our research is continuing; our knowledge expanding. Vaccines are now available and offer hope to end the pandemic.

This study is important as it helps us understand the severity of the virus, and builds evidence to determine what is the greater public health priority. COVID-19 has strained healthcare systems around the world, forcing governments to implement unprecedented measures to help contain the spread. Have these measures been too strict? Time will tell.


Resources

Auvinen R et al; Comparison of the clinical characteristics and outcomes of hospitalized adult COVID-19 and influenza patients - a prospective observational study. Infect Dis (Lond). 2020 Nov 10:1-11. doi: 10.1080/23744235.2020.1840623. Epub ahead of print. PMID: 33170050.

Iuliano AD et al; Global Seasonal Influenza-associated Mortality Collaborator Network. Estimates of global seasonal influenza-associated respiratory mortality: a modelling study. Lancet. 2018 Mar 31;391(10127):1285-1300. doi: 10.1016/S0140-6736(17)33293-2. Epub 2017 Dec 14. Erratum in: Lancet. 2018 Jan 19;: PMID: 29248255; PMCID: PMC5935243.

Piroth L et al; Comparison of the characteristics, morbidity, and mortality of COVID-19 and seasonal influenza: a nationwide, population-based retrospective cohort study. Lancet Respir Med. 2020 Dec 17:S2213-2600(20)30527-0. doi: 10.1016/S2213-2600(20)30527-0. Epub ahead of print. PMID: 33341155.

Pormohammad A et al; Comparison of influenza type A and B with COVID-19: A global systematic review and meta-analysis on clinical, laboratory and radiographic findings. Rev Med Virol. 2020 Oct 9:e2179. doi: 10.1002/rmv.2179. Epub ahead of print. PMID: 33035373; PMCID: PMC7646051.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Sam Porter

Comments

Sam Porter (author) from France on January 25, 2021:

Thank you Tanith

Tanith on January 22, 2021:

Written in earnest and disclosing a wealth of facts and knowledge . Bravo to the author . Let’s hope that 2021 leads us to a more positive publication .

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