University of Edinburgh: Covid-19 with flu increases risk of death

Adults in hospital who have Covid-19 and the flu at the same time are at much greater risk of severe disease and death compared with patients who have Covid-19 alone or with other viruses, research shows.
Patients with co-infection of SARS-CoV-2, which causes Covid-19, and influenza viruses were over four times more likely to require ventilation support and 2.4 times more likely to die than if they only had Covid-19, experts found.

Researchers say the findings show the need for greater flu testing of Covid-19 patients in hospital and highlight the importance of full vaccination against both Covid-19 and the flu.

Hospitalised patients
The team from the University of Edinburgh, University of Liverpool, Leiden University and Imperial College London, made the findings in a study of more than 305,000 hospitalised patients with Covid-19.

The research – delivered as part of the International Severe Acute Respiratory and emerging Infection Consortium’s (ISARIC) Coronavirus Clinical Characterisation Consortium – is the largest ever study of people with Covid-19 and other endemic respiratory viruses.

ISARIC’s study was set up in 2013 in readiness for a pandemic such as this.

Co-infections
The team looked at the data of adults who had been hospitalised with Covid-19 in the UK between 6 February 2020 and 8 December 2021.

Test results for respiratory viral co-infections were recorded for 6965 patients with Covid-19. Some 227 of these also had the influenza virus, and they experienced significantly more severe outcomes.

In the last two years we have frequently witnessed patients with Covid-19 become severely ill, at times leading to an ICU admission and the employment of an artificial ventilator to help with breathing. That an influenza infection could give rise to a similar situation was already known, but less was understood about the outcomes of a double infection of SARS-CoV-2 and other respiratory viruses.

Dr Maaike Swets
PhD student at the University of Edinburgh and Infectious Diseases department, Leiden University Medical Centre
We found that the combination of Covid-19 and flu viruses is particularly dangerous. This will be important as many countries decrease the use of social distancing and containment measures. We expect that Covid-19 will circulate with flu, increasing the chance of co-infections. That is why we should change our testing strategy for Covid-19 patients in hospital and test for flu much more widely.

Professor Kenneth Baillie
Professor of Experimental Medicine at the University of Edinburgh
The findings have been published in The Lancet. Research letters published in the Correspondence section of The Lancet include research findings and are externally peer-reviewed. Unlike Articles containing original data, research letters are shorter and the research they contain is usually preliminary, exploratory, or reporting on early findings.

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