How to Tell the Difference Between COVID-19 and Flu Symptoms (Because They Can Look Very Similar)

Believe it or not, this year will be the third winter we've had to navigate COVID-19. And despite vaccines being widely available to adults in the United States, vaccination rates are nowhere close to where they need to be for the pandemic to really let up. This means that we're in store for another tricky cold and flu season, where it might be difficult to tell the difference between symptoms of the flu versus COVID-19.

We'd love to be able to tell you that there's always a surefire way to differentiate between COVID and flu symptoms, but in large part, there isn't—and that's part of what makes the coronavirus so sneaky. But what we can provide you with is expert advice on the symptoms of the flu and COVID-19, and what to consider when you're feeling under the weather. Here's what to know and tips to help you know the difference (and when to check in with a doctor).

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Flu symptoms vs. COVID-19 symptoms: Similarities and Differences

The challenge with asking about the differences between symptoms of the flu and COVID-19 is that there are actually very few. In fact, both viral conditions share a set of overlapping symptoms, which, according to the Centers for Disease Control and Prevention (CDC) include:

• Fever or feeling feverish/having chills

• Cough

• Shortness of breath or difficulty breathing

• Fatigue (tiredness)

• Sore throat

• Runny or stuffy nose

• Muscle pain or body aches

• Headache

• Vomiting and diarrhea

The CDC, as well as the doctors we spoke with, do note that while a change or loss in taste and/or smell is more commonly associated with COVID-19, it can also happen with other illnesses, like the flu or a sinus infection. Plus, as Suzanne Ferree Turner, MD, a family medicine physician and the founder of Vine Medical Associates in Roswell, Ga., points out, it's also entirely possible to have COVID-19 without losing your sense of taste and/or smell.

"When upper respiratory symptoms like cough, runny nose, and fever hit, it is very difficult at first to know if you are dealing with a cold, the flu or COVID," says David Cutler, MD, a family medicine physician at Providence Saint John's Health Center in Santa Monica, Calif. "There may be hints—like loss of taste and smell suggesting COVID, high fever and body aches suggesting flu, sore throat and runny nose without fever suggesting a simple cold—but these symptomatic clues are far from certain."

According to Dr. Turner, although the flu and COVID-19 look very similar for the first two to four days of the illness, there are subsequent clues that may help differentiate between the two. "The flu typically starts suddenly and is full-blown one to four days after exposure; the flu tends to resolve in three to seven days," she explains. "COVID may have a longer 'runway' — up to 14 days after exposure, and COVID has a three-to-seven-day 'smoldering case,' with worsening on days four to seven after symptom onset. Either viral infection can cause illness and can, in at-risk populations, result in pneumonia and death."

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Flu and COVID symptoms you shouldn't ignore

Some symptoms of the flu and COVID should always be taken seriously, because regardless of your official diagnosis, they can be potentially dangerous.

"There are certainly symptoms for either disease that warrant medical attention," Jordan Smith, PharmD, assistant professor of clinical sciences at High Point University says. "If patients are otherwise healthy and have mild symptoms—like fever, cough, sore throat, fatigue, headache, aches and pains, loss of taste and smell—they can take precautionary measures like staying home, wearing masks, and resting. However, if those symptoms are accompanied by shortness of breath, persistent pain or pressure in the chest, new confusion, inability to sleep or stay awake, or pale skin, the patient should seek immediate medical attention."

Additionally, people over the age of 65, or those who have cardiovascular disease, chronic lung diseases (like asthma), diabetes, cancer, or chronic kidney disease, those who are immunosuppressed, those who smoke cigarettes, and those who are pregnant are also at increased risk of complications and should be especially careful of looking out for problem symptoms, Dr. Smith notes. "Patients should stay home when they're sick, separate themselves from others as much as possible, and call their doctor or local health department if they feel symptoms are getting worse and/or include any of those mentioned above," he adds.

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The flu and COVID-19: What to know about testing and the spread of the viruses

All the similarities between flu and COVID-19 symptoms may leave you wondering why knowing which condition you have even matters. Although you should stay home from work or school, isolate as much as possible, and practice social distancing and mask-wearing if you experience any of the symptoms above (you really don't want to pass either COVID or flu to others), it's important to keep in mind that COVID is exceptionally transmissible, even more so than flu—and even when a person is asymptomatic and feeling fine.

"While the virus that causes COVID-19 and flu viruses are thought to spread in similar ways, the virus that causes COVID-19 is generally more contagious than flu viruses," says Jennifer Caudle, DO, a family medicine physician. "Also, COVID-19 has been observed to have more superspreading events than flu. This means the virus that causes COVID-19 can quickly and easily spread to a lot of people and result in continual spreading among people as time progresses."

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And this is where COVID testing comes in. "Because some of the symptoms of flu, COVID-19, and other respiratory illnesses are similar, the difference between them cannot be made based on symptoms alone, according to the CDC," Dr. Caudle explains. "Testing is needed to tell what the illness is and to confirm a diagnosis."

Not only that, but it's possible to be infected with both the flu and the virus that causes COVID-19 at the same time—which makes all the overlapping symptoms even more confusing. "For signs of flu-like symptoms, it is best to get tested for both the flu and COVID-19 to determine accordingly, and understand necessary next steps to best recover," Dr. Caudle says.

There are a number of factors that could impact the results of a flu or COVID-19 test—including the type of test and when in the course of the illness you take it—but getting tested and having some idea of the virus that's making you sick can help prevent you from spreading it to other people. As Dr. Cutler points out, rapid testing can be very helpful, but has limitations thanks to higher rates of false positive and false negative results. If possible, get a polymerase chain reaction (PCR) COVID-19 test, because it is more reliable and accurate, according to the Cleveland Clinic, and can detect the virus in your body within a longer time frame.

And in case you need another reason to get tested and do whatever you can to prevent the continued spread of COVID-19, doing so can ultimately lead to fewer variants of the virus, like the Alpha, Beta, and Delta strains that have caused so much concern over the past several months.

"The replication of the COVID virus inside any infected person could give rise to such variants," Dr. Cutler explains. "This fact provides an additional imperative for every eligible person to be vaccinated against COVID. And while these new variants may differ somewhat in transmissibility and severity, distinguishing them from older variants can only be done by time-consuming, detailed genetic analysis."

How to prepare for the upcoming flu season

Thanks to a number of factors—including mask-wearing and social distancing—the most recent flu season was remarkably mild. But given how much has changed in terms of relaxing public health measures, and people once again venturing out of their homes on a regular basis, what does the upcoming flu season look like?

"The obvious prediction is that the incidence of infections [other than COVID-19] will increase," Dr. Cutler explains. "After a worldwide drop in influenza cases, and the lowest rate on record in the United States during the pandemic, we should all expect to see more flu in the coming fall and winter. So it will be very important for everyone to get their flu vaccines."

Ultimately, regardless of what type of virus (or other pathogen) made you sick, your best bet is to do what you can to prevent your illness from spreading to other people.

"The bottom line is that the diseases are similar enough that, especially for the coming year, patients suspicious they are ill with either of them should take care of themselves, stay home from work, and take precautionary measures to avoid the spread of disease to family, friends, and coworkers," Dr. Smith says. "Thankfully, mask wearing, social distancing, and avoiding public spaces all work well to prevent the spread of both diseases."

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