Can flu virus affect SARS-CoV-2 severity?

Coinfection of SARS-CoV-2 and influenza A virus changes neither the trajectory nor the severity of influenza A virus, regardless of timing. But if a person contracts influenza A virus first, the response to that infection can significantly suppress SARS-CoV-2, according to research.

"The research is important because the human population now has two circulating respiratory RNA viruses with high pandemic potential: SARS-CoV-2 and influenza A," said researchers from the New York University, Langone.

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"As both viruses infect the airways, and can result in significant morbidity and mortality, it is imperative that we also understand the consequences of coinfection," they added.

Several clinical studies had previously reported on co-infection of SARS-CoV-2 with other viruses.

These viruses infect the same cells within the airway.

Notably, the influenza A virus interferes with SARS-CoV-2 replication in the lung and can continue to do so even more than one week after clearance of influenza A, according to the research published in the Journal of Virology.

"These data suggest the presence of factors intrinsic to or induced by (influenza A virus) that may restrict the growth of SARS-CoV-2, but it remains unclear whether this effect plays a role on disease severity," the researchers wrote.

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The investigators performed the experiments in cultured cells, as well as in a golden hamster animal model. "Animals were administered the 2 viruses simultaneously, and examined at days 1,3, 5, 7 and 14 post-infection," said corresponding author Benjamin R tenOever, Professor of microbiology, at NYU.

The researchers also conducted experiments in which they first challenged the animals with either virus, followed three days later by the other virus, monitoring (them) on days 1, 3, and 5 post-second challenge.

"This study could be used as an example of how an immune response to something unrelated can provide protection against SARS-CoV-2," said tenOever.

The team demonstrated that coinfection does not result in a worse outcome of disease in an animal model. These results suggest that coinfection with SARS-CoV-2 and influenza A virus does not represent a looming threat for humanity," said tenOever.