9 Citations (Scopus)


BACKGROUND: The impact of SARS-CoV-2 alongside influenza is a major concern in the northern hemisphere as winter approaches. 

METHODS: Test data for influenza and SARS-CoV-2 from national surveillance systems between 20 January 2020 and 25 April 2020 were used to estimate influenza infection on the risk of SARS-CoV-2 infection. A test-negative design was used to assess the odds of SARS-CoV-2 in those who tested positive for influenza compared with those who tested negative. The severity of SARS-CoV-2 was also assessed using univariable and multivariable analyses. 

RESULTS: The risk of testing positive for SARS-CoV-2 was 58% lower among influenza-positive cases and patients with a coinfection had a risk of death of 5.92 (95% confidence interval: 3.21-10.91) times greater than among those with neither influenza nor SARS-CoV-2. The odds of ventilator use or death and intensive care unit admission or death were greatest among coinfected patients. 

CONCLUSIONS: Coinfection of these viruses could have a significant impact on morbidity, mortality and health-service demand.

Original languageEnglish
Pages (from-to)1124-1133
Number of pages10
JournalInternational Journal of Epidemiology
Issue number4
Early online date3 May 2021
Publication statusPublished - Aug 2021

Bibliographical note

Funding Information: The work was supported by authors at Public Health England as part of the routine functions of surveillance and control of communicable diseases. Public Health England, National Infection Service, Immunisation and Countermeasures Division has provided vaccine manufacturers with post-marketing surveillance reports, which the Marketing Authorisation Holders are required to submit to the UK licensing authority in compliance with their Risk Management Strategy. A cost recovery charge is made for these reports.

Open Access: This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits
unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Publisher Copyright: © The Author(s) 2021. Published by Oxford University Press on behalf of the International Epidemiological Association.

Citation: Julia Stowe, Elise Tessier, H Zhao, Rebecca Guy, Berit Muller-Pebody, Maria Zambon, Nick Andrews, Mary Ramsay, Jamie Lopez Bernal, Interactions between SARS-CoV-2 and influenza, and the impact of coinfection on disease severity: a test-negative design, International Journal of Epidemiology, Volume 50, Issue 4, August 2021, Pages 1124–1133,

DOI: https://doi.org/10.1093/ije/dyab081


  • SARS-CoV-2
  • coinfection
  • epidemiology
  • influenza
  • interaction


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