International

Lancet: COVID far deadlier than influenza

28/12/2020

Background

To date, influenza epidemics have been considered suitable for use as a model for the COVID-19 epidemic, given that they are respiratory diseases with similar modes of transmission. However, data directly comparing the two diseases are scarce.

Methods

We did a nationwide retrospective cohort study using the French national administrative database (PMSI), which includes discharge summaries for all hospital admissions in France. All patients hospitalised for COVID-19 from March 1 to April 30, 2020, and all patients hospitalised for influenza between Dec 1, 2018, and Feb 28, 2019, were included. The diagnosis of COVID-19 (International Classification of Diseases [10th edition] codes U07.10, U07.11, U07.12, U07.14, or U07.15) or influenza (J09, J10, or J11) comprised primary, related, or associated diagnosis. Comparisons of risk factors, clinical characteristics, and outcomes between patients hospitalised for COVID-19 and influenza were done, with data also stratified by age group.

Findings

89 530 patients with COVID-19 and 45 819 patients with influenza were hospitalised in France during the respective study periods. The median age of patients was 68 years (IQR 52–82) for COVID-19 and 71 years (34–84) for influenza. Patients with COVID-19 were more frequently obese or overweight, and more frequently had diabetes, hypertension, and dyslipidaemia than patients with influenza, whereas those with influenza more frequently had heart failure, chronic respiratory disease, cirrhosis, and deficiency anaemia. Patients admitted to hospital with COVID-19 more frequently developed acute respiratory failure, pulmonary embolism, septic shock, or haemorrhagic stroke than patients with influenza, but less frequently developed myocardial infarction or atrial fibrillation. In-hospital mortality was higher in patients with COVID-19 than in patients with influenza (15 104 [16·9%] of 89 530 vs 2640 [5·8%] of 45 819), with a relative risk of death of 2·9 (95% CI 2·8–3·0) and an age-standardised mortality ratio of 2·82. Of the patients hospitalised, the proportion of paediatric patients (<18 years) was smaller for COVID-19 than for influenza (1227 [1·4%] vs 8942 [19·5%]), but a larger proportion of patients younger than 5 years needed intensive care support for COVID-19 than for influenza (14 [2·3%] of 613 vs 65 [0·9%] of 6973). In adolescents (11–17 years), the in-hospital mortality was ten-times higher for COVID-19 than for influenza (five [1·1% of 458 vs one [0·1%] of 804), and patients with COVID-19 were more frequently obese or overweight.

Interpretation

The presentation of patients with COVID-19 and seasonal influenza requiring hospitalisation differs considerably. Severe acute respiratory syndrome coronavirus 2 is likely to have a higher potential for respiratory pathogenicity, leading to more respiratory complications and to higher mortality. In children, although the rate of hospitalisation for COVID-19 appears to be lower than for influenza, in-hospital mortality is higher; however, low patient numbers limit this finding. These findings highlight the importance of appropriate preventive measures for COVID-19, as well as the need for a specific vaccine and treatment.

Funding

French National Research Agency.

Introduction

In December, 2019, a new disease now known as COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged as a major world threat. Considering its ability to spread and the relatively low case-fatality rates initially reported in China, SARS-CoV-2 was thought to be more similar to influenza than SARS-CoV-1.¹The preventive measures for this new infection were based on a comparison with the influenza virus because the viruses have similar modes of transmission and cause respiratory disease. Patients with COVID-19 were also anticipated to benefit from the clinical knowledge and care management of influenza.

A global pandemic was declared on March 11, 2020. By July 10, 2020, more than 12 million cases of COVID-19 and 554 000 COVID-19-related deaths had been identified worldwide. In France, it had already caused more than 30 000 deaths, nearly 20 000 of which were in hospital.²At this point, COVID-19 had developed into a pandemic associated with substantial morbidity and mortality, putting great strain on hospitals and the health system in generall

Research in context
Evidence before this study

We searched PubMed with the terms “COVID-19” and “influenza” for articles in any language published up to July 16, 2020, that compared clinical characteristics, intensive care unit (ICU) admission, morbidity, and mortality of patients hospitalised for COVID-19 and for seasonal influenza. After excluding co-infection studies and studies of influenza pandemics, we identified five studies. An international study compared comorbidity and previous medications in adult patients (≥18 years) hospitalised either for COVID-19 or for seasonal influenza over the 2014–19 period. Another study focused on the risk of ischaemic stroke, including ICU admission and in-hospital mortality, of adult patients visiting emergency departments or hospitalised for COVID-19 in 2020 in two New York hospitals compared with adult patients with seasonal influenza from 2016 to 2018. The three other studies identified by our search had smaller populations. One small study was done in a French hospital and compared adult patients, and another focused on children younger than 1 year, comparing those hospitalised for influenza in the past few years to published features of COVID-19 in low-income and middle-income countries. Finally, another small study compared the clinical characteristics and treatments of children under the age of 5 years hospitalised in Wuhan for COVID-19 or influenza. Therefore, little information is available on the comparative burden of COVID-19 and seasonal influenza, particularly in children, who are considered to be at low risk of severe disease.