Published: 28 March 2022
Patients in hospital with both COVID-19 and flu are at much greater risk of severe disease and death, new NIHR-funded and supported research shows.
The findings, from a study carried out by the University of Edinburgh, University of Liverpool, Leiden University and Imperial College London, show patients who were infected with SARS-CoV-2 (the virus which causes COVID-19) and influenza at the same time 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.
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.
The research, published in The Lancet, included more than 305,000 hospitalised patients with COVID-19. It was delivered as part of the International Severe Acute Respiratory and emerging Infection Consortium’s (ISARIC) Coronavirus Clinical Characterisation Consortium – 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.
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.
Dr Maaike Swets, PhD student at the University of Edinburgh and Leiden University, said: “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.”
Professor Kenneth Baillie, Professor of Experimental Medicine at the University of Edinburgh, said: “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 Calum Semple, Professor of Outbreak Medicine and Child Health at the University of Liverpool, said: “We are seeing a rise in the usual seasonal respiratory viruses as people return to normal mixing. So, we can expect flu to be circulating alongside Covid-19 this winter. We were surprised that the risk of death more than doubled when people were infected by both flu and Covid-19 viruses. It is now very important that people get fully vaccinated and boosted against both viruses, and not leave it until it is too late.”