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Flu vs. Covid: Ways to Identify Symptoms and Differences

The Wall Street Journal. logo The Wall Street Journal. 9/14/2020 Alina Dizik
a bunch of office supplies © Jeffrey Greenberg/Getty Images

As the autumn flu season approaches while the Covid-19 pandemic continues, cold-weather sniffles are likely to provoke even more anxiety than usual. Some symptoms of flu—as well as colds and other autumn ailments—are similar to Covid’s, making it harder to know what’s wrong. Fever, dry cough, fatigue and body aches are common with both the flu and Covid.

If you’re concerned, call your doctor. And there are some ways to try to recognize the differences. Here’s what doctors say.

Can you differentiate between illnesses by tracking your fever?

Fever is common in Covid-19, and also likely to appear with the flu and other viruses. But fevers that result from the novel coronavirus tend to come on stronger and cause chills and major discomfort even if they don’t climb far past 100.4 degrees, says Panagis Galiatsatos, a physician in pulmonary and critical care medicine at the Johns Hopkins School of Medicine in Baltimore. “Covid-19 fevers are not subtle,” he says. “Look beyond the number to see how the fever is making you feel.”

Does the speed of onset vary between Covid-19 and flu?

How quickly you come down with symptoms may be telling for some people, especially for those who can pinpoint their day of exposure. Coronavirus symptoms often come on suddenly around day five to seven, but can appear as long as 14 days after exposure. Those who have the flu tend to experience symptoms one to four days after exposure, says Molly Fleece, an infectious disease specialist at the University of Alabama at Birmingham.

If you’re staying home to monitor your symptoms, what are the signs that might point to Covid-19?

As the virus progresses, it can be easier to tell whether it’s Covid-19 or another illness, says Ben Singer, pulmonary and critical care specialist at Northwestern Medicine in Chicago. Among the most telltale indications of Covid-19 are shortness of breath, pneumonia and continued fever. “If people are at home monitoring their symptoms, the thing to look out for is that things are generally getting worse,” Dr. Singer says.

Sneezing and a stuffy nose are often associated with a cold. Can nasal congestion be a sign of Covid-19?

Yes, but it’s less likely. The good news is that most colds start with nasal congestion, but it’s not one of the primary symptoms of Covid-19, says Dr. Fleece. A stuffy nose is also less worrisome if that’s the only symptom you have, she adds. Having Covid-19 with “just a runny nose is probably unlikely,” she adds.

Another symptom that’s more prevalent with a cold: a wet cough where phlegm is involved. On the other hand, a dry cough or especially a loss of smell or taste can be symptomatic of Covid-19, she adds.

How important is it that I get a flu shot this year?

It is very important. Even if you do get sick with the flu, the vaccine can lessen the duration and severity of the illness. That helps keep you out of the ER, decreasing the strain on the health care system when doctors are trying to fight Covid. And your getting vaccinated helps prevent the spread to others, including infants and other medically vulnerable people who can’t get a flu shot.

Will this year’s flu shot help boost immunity for Covid-19?

There’s no evidence that the flu vaccine can help protect you from Covid-19. But generally, “vaccines strengthen, not weaken, the immune system,” says David Beuther, chief medical information officer at National Jewish Health in Denver. “The more you’ve been vaccinated in recent years, the better trained your immune system is.”

Will getting the flu shot make it easier to tell the difference between flu and Covid-19?

Whether you’ve had your flu shot will be one of the top questions physicians ask in screening for Covid-19 symptoms, helping doctors make a correct diagnosis. “The flu shot is really important this year,” says Dr. Beuther. “It can significantly reduce your chance of influenza, and reduce the chance that you’ll be in this conundrum.”

Does having the flu make you more vulnerable to Covid-19? Can you get them at the same time?

It’s possible that having a severe case of flu could make you more vulnerable to another illness, including Covid, says Dr. Galiatsatos. But since Covid is so new, not much is known about how one might affect the other.

If you do happen to get both flu and Covid at the same time, your illness may be more severe. “A second viral infection might warrant closer monitoring of a patient for deterioration,” says Dr. Beuther. During flu season, most people will be tested for multiple viruses, including Covid-19, to help doctors gain a clearer picture, he adds.

What can you glean from local health data to better evaluate your symptoms?

Local health departments often post data about a variety of illnesses to help medical providers. Along with the flu, looking at increases for other viruses in your area including RSV (Respiratory syncytial virus) and parainfluenza can make it easier to interpret symptoms, says James Cherry, a professor at the David Geffen School of Medicine at University of California Los Angeles. “You have to think about epidemiology and what else is around now,” he says.

Write to Alina Dizik at


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