COVID-19 has killed about 180,000 Americans, and the Centers for Disease Control and Prevention estimate influenza causes up to 61,000 deaths in the U.S. annually.
As the flu season approaches, experts are voicing concerns about what might happen when the two overlap.
They also say the convergence highlights why it is vital that everyone gets a flu shot.
When the flu sends its usual hundreds of thousands of patients to hospitals this year, it will further tax a health care system exhausted by an ongoing, and possibly resurgent, pandemic.
Differences in disease progression, spread and treatment underline the need for effective widespread testing, but beyond that, too many unknowns remain to say anything definitive.
"We have our local philosopher here in New York, which is Yogi Berra, and he said, 'It's difficult to make predictions, especially about the future,'" said Peter Palese, a microbiologist and influenza expert at New York's Icahn School of Medicine at Mount Sinai.
SARS-CoV-2 and influenza have already co-occurred in the temperate areas of the Southern Hemisphere, where flu season runs from April to September. Flu occurs year-round in the tropics.
But this year's Southern Hemisphere flu season has been mild.
Some credit socials distancing measures, although masks do not protect against flu the way they do against coronavirus. Others suggest the body's immune response to the SARS-CoV-2 might help fight off flu as a side-effect. Still others say the lack of cases arises from undercounts caused by people avoiding hospitals during the pandemic.
Ultimately, insufficient data cannot support any firm forecasts, positive or negative, for such an unprecedented event.
"There is no good evidence to go either way, and I think the past is not a good indicator for the future," said Palese.
