US Pharm. 2022;47(4):1.

Adults in the hospital with COVID-19 and simultaneous influenza are at much greater risk of severe disease and death compared with patients who have COVID-19 alone or with other viruses, new research from the United Kingdom shows. Patients with coinfection of SARS-CoV-2 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, the experts found.

The researchers say the findings, published in The Lancet, show the need for greater influenza testing of COVID-19 patients in hospitals and highlight the importance of full vaccination against both COVID-19 and the flu. The 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. Test results for respiratory viral coinfections were recorded for 6,965 patients with COVID-19. Some 227 of these also had the influenza virus, and they experienced significantly more severe outcomes.

Maaike Swets, PhD student at the University of Edinburgh and Leiden University, said, “In the last 2 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.”

Echoing Ms. Swets’ comments, 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 coinfections. That is why we should change our testing strategy for COVID-19 patients in hospital and test for flu much more widely.”

The stark relationship between COVID-19 and influenza infections and severe outcomes came as a surprise to Calum Semple, professor of outbreak medicine and child health at the University of Liverpool. “We are seeing a rise in the usual seasonal respiratory viruses as people return to normal mixing,” he said. “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.”

Geert Groeneveld, doctor at Leiden University Medical Center’s infectious diseases department, characterized the ramifications for inpatient treatment regimens. “Understanding the consequences of double infections of SARS-CoV-2 and other respiratory viruses is crucial.”

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