COVID-19 and the flu can increase severe risks, including death

As we learn to live with the Covid-19 virus, researchers are working to better understand its impacts. A new study has revealed that adults sick with both Covid-19 and the flu simultaneously are at a much greater risk of severe disease or even death compared to patients infected with Covid alone. 

A research team from the University of Edinburgh, University of Liverpool, Leiden University and Imperial College London, studied more than 305,000 hospitalized patients with Covid-19. It is the largest ever study of people with Covid-19 and other endemic respiratory viruses.

“Understanding the consequences of double infections of SARS-CoV-2 and other respiratory viruses is crucial as they have implications for patients, hospitals and ICU capacity during seasons that SARS-CoV-2 and influenza circulate together,” said Dr. Geert Groeneveld of Leiden University Medical Center.

For the investigation, test results for respiratory viral co-infections were recorded for 6,965 Covid-19 patients. Of these, 227 also had the flu and were experiencing more significant symptoms. 

Patients with co-infection of Covid-19 and flu 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.

The study demonstrates a greater need for flu testing of hospitalized Covid-19. It also demonstrates the importance of staying diligent with flu shots and full vaccination against Covid-19.

A representative from each research team shared their observations on the threat of co-infection. 

“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,” said Dr. Maaike Swets, PhD student at the University of Edinburgh.

“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,” said Kenneth Baillie, professor of Experimental Medicine at the University of Edinburgh. “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 of the University of Liverpool, noted that there has been 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.”

“Being infected with more than one virus is not very common but it’s important to be aware that co-infections do happen,” said Professor Peter Openshaw of Imperial College London. “The vaccines that protect against Covid-19 and flu are different, and people need both. The way that these two infections are treated is also different so it’s important to test for other viruses even when you have a diagnosis in someone who is hospitalised with a respiratory infection. This latest discovery by the ISARIC consortium again adds significantly to improving the way we manage patients.”

The research was funded by UK Research and Innovation (UKRI) and by the Department of Health and Social Care through the National Institute for Health Research (NIHR) as part of the UK Government’s Covid-19 rapid research response. It is published in the journal The Lancet

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By Katherine Bucko, Earth.com Staff Writer