Flu Season Looms And Scientists Wonder How Flu And COVID-19 Might Mix

With the annual flu season about to start, it's still unclear exactly how influenza will interact with COVID-19 if a person has both viruses.

Doctors around the world have seen some patients who tested positive for both the influenza virus and the coronavirus that causes COVID-19. At least a couple dozen cases have been reported—although that's not a lot, considering that over 26 million people have tested positive for SARS-CoV-2, the virus that causes COVID-19.

Still, "it is quite possible and likely that the two viruses could infect a patient at the same time, or for that matter sequentially: one month, one virus, and the next month, the other virus," says Michael Matthay, a professor of medicine at the University of California, San Francisco.

Both viruses can cause dangerous inflammation in the lungs that can fill the airspaces with fluid, making it difficult to breathe, he notes.

"It's likely with both viruses at the same time, the severity of respiratory failure would be greater," says Matthay. "Or, of course, having two illnesses in a row that affected the lungs would make the respiratory failure more severe."