COVID-19, flu an especially dangerous pair

Mechanically ventilated patient
Mechanically ventilated patient

Georgiy Datsenko / iStock

Adult COVID-19 patients also infected with the flu are four times more likely to require mechanical ventilation and 2.4 times more likely to die than if they had COVID-19 alone, finds a UK study published late last week in The Lancet.

In the largest study of patients with both COVID-19 and other respiratory viruses thus far, a team led by University of Edinburgh researchers studied the clinical outcomes of 583 adult COVID-19 patients also infected with flu viruses, respiratory syncytial virus (RSV), or adenoviruses who were hospitalized from Feb 6, 2020, to Dec 8, 2021, well before the emergence of the Delta and Omicron variants.

The study, conducted as part of the International Severe Acute Respiratory and Emerging Infection Consortium's Coronavirus Clinical Characterisation Consortium, was set up in 2013 to be ready for a pandemic such as this one.

Of the 583 COVID-19 patients, 277 also had the flu, 220 had RSV, and 136 were infected with an adenovirus, such as those that cause the common cold, conjunctivitis, croup, bronchitis, or pneumonia.

Need for routine flu testing in COVID patients

Coinfection with COVID-19 and the flu was associated with a greater likelihood of needing mechanical ventilation (weighted odds ratio [OR], 4.14) and in-hospital death (OR, 2.35). In contrast, weighted ORs for RSV and adenovirus, respectively, were 0.78 and 0.64 for mechanical ventilation and 0.60 and 1.53 for death.

In a University of Edinburgh press release, senior author Kenneth Baillie, MBChB, PhD, said that the study findings will be important as many countries reduce the use of COVID-19 public health measures such as physical distancing.

"We expect that Covid-19 will circulate with flu, increasing the chance of co-infections," he said. "That is why we should change our testing strategy for Covid-19 patients in hospital and test for flu much more widely."

The researchers called for further promotion of COVID-19 and flu vaccinations, as well as testing of hospitalized COVID-19 patients for the flu to identify at-risk patients and those who might have different responses to immune system-modifying and antiviral treatments. "It is now very important that people get fully vaccinated and boosted against both viruses, and not leave it until it is too late," coauthor Calum Semple, PhD, of the University of Liverpool, said in the release.

Coauthor Peter Openshaw, MBBS, of Imperial College London, said that viral coinfections are rare but do occur and that vaccinations against COVID-19 and the flu are a must because the two work in very different ways. "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," he said.

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