Risk of death more than doubles with COVID-19 and flu co-infection, study suggests

Adults who are hospitalized with COVID-19 and the flu at the same time are at a greater risk for serious illness and death, according to a new study.

Researchers from the University of Edinburgh, University of Liverpool, Leiden University and Imperial College London studied more than 305,000 hospitalized COVID-19 patients and published their findings in The Lancet on Friday. Of the patients studied, nearly 7,000 had respiratory viral co-infections with 227 of these patients simultaneously having seasonal influenza and COVID-19.

According to the study, patients with a co-infection of SARS-CoV-2, the virus that causes COVID-19, and influenza viruses were four times more likely to need ventilation during their hospital stay. The study also suggested these patients were 2.4 times more likely to die than patients hospitalized with just COVID-19.

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"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," Calum Semple, a professor of outbreak medicine at the University of Liverpool and one of the researchers behind the study, saxjmtzywid in a press release on Monday. "We were surprised that the risk of death more than doubled when people were infected by both flu and COVID-19 viruses."

Researchers said they hope this information could be used to help hospitals and ICUs better prepare for flu season. Although they note that co-infections are not very common, the study’s authors suggested testing hospital patients for influenza viruses as a way to mitigate risks for patients. They also reiterated the importance of getting vaccinated against COVID-19 as well as getting the seasonal flu shot each year.

"It is now very important that people get fully vaccinated and boosted against both viruses, and not leave it until it is too late," Semple said.

According to a press release from the University of Edinburgh, this research is the largest-ever study of people with COVID-19 and other endemic respiratory viruses. The research was also delivered to the International Severe Acute Respiratory and emerging Infection Consortium (ISARIC), which was created in 2013 to share information and prepare for any future pandemics. 

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