The flu virus itself is nothing to fool with.

The Centers For Disease Control and Prevention says 8% of the U.S. population — about 26 million people — get the flu each year.

Both viruses at the same time can make you very sick.

But Dr. Rhame said there’s another problem.

“If you have COVID, you’re way worse off if you also have influenza,” he said. “If you get influenza, we’re going to test you, and if you have influenza, we’ve wasted a COVID test. We don’t have enough COVID tests.”

So how do you tell if you’ve got COVID or the flu?

The biggest difference, Dr. Rhame said, is the tempo of the viruses, the speed at which they begin attacking the body.

Flu symptoms — cough, fever, and sore throat — can appear in hours.

“Influenza starts very fast,” Dr. Rhame said. “The classic cases, you feel good in the morning, and in the afternoon, you feel like a Mack truck hit you.”

But COVID is more subtle.

You might feel lousy but full-blown symptoms might not appear for three or four days. 

"COVID sneaks up on you, so even though you have the onset of symptoms, it may be a day or two before you admit to yourself that something's wrong,” Dr. Rhame noted.

Other COVID warning signs, like diarrhea and vomiting, can appear with the flu but are more likely with COVID. 

And then, there’s perhaps the strangest COVID symptom of all: the loss of smell.

"Although you can lose your sense of smell with influenza, it's because you have a nose full of mucus,” Dr. Rhame said. “Whereas with COVID, it's because the virus is actually attacking the cells up there, what you smell with."

Dr. Rhame said if you are starting to feel sick, don’t rush out to get tested.

He said, instead, it’s a good idea to call a triage nurse.

"Every health care system has a triage nurse,” according to Dr. Rhame. “These folks are trained to ask a set of questions and make a conclusion about what you should do next."

Yet, amid all this concern about COVID and the flu, there may be some good news.

Dr. Rhame said flu outbreaks in the southern hemisphere, now emerging from its winter season, appear to have fallen because of COVID safe-distancing, extreme cleaning and other measures.

"There was a way substantial reduction in the amount of influenza in the southern hemisphere,” he said. “We presume to a certain extent because a lot of people were taking COVID precautions.”

Still, Dr. Rhame said all Americans, including Minnesotans, need to continue precautions.

He said most people should think twice before using elevators, for example.

“Airborne droplets, the ones that float through the air, that can be left after he leaves,” he explained. “They are worst in a confined space, with small spaces and bad ventilation. That’s elevators.”

Dr. Rhame added that what makes COVID especially concerning is that it may be even more contagious a day or two before symptoms appear. That makes it hard to isolate people promptly. 

He advises everyone to get a flu shot, especially this year.

“If you get both illnesses at once, it is way worse,” he said. “You don’t want to get both at the same time.”