Flu vs. COVID vs. RSV Symptoms: How to Tell the Difference

Medically reviewed by Keith Seibert, MD  |  Last Reviewed: September 2026

Quick Answer Flu, COVID-19, and RSV can look nearly identical at first — all three cause fever, cough, congestion, and fatigue. The clearest tip-offs: flu tends to hit hard and fast with a high fever (103–104°F) and body aches, COVID-19 is more likely to cause loss of taste or smell and can bring on lingering “brain fog,” and RSV is more likely to cause wheezing and is especially concerning in infants and older adults. Because symptoms overlap so much, testing is the only reliable way to know which virus you’re dealing with — and it matters, since flu and COVID-19 both have antiviral treatments that work best when started early.

Why It’s So Hard to Tell Them Apart

Flu, COVID-19, and RSV are all respiratory viruses that spread the same way — through droplets from coughing, sneezing, and talking — and all three tend to circulate most heavily from fall through late winter. That overlap in timing and symptoms is exactly why so many people search “is this the flu or something else” every October. Knowing the subtle differences can help you decide how urgently to seek care, but a test is still the only way to know for certain.

As Cleveland Clinic notes, telling these three apart by symptoms alone is genuinely difficult — which is exactly why the comparison below is meant as a general guide, not a diagnosis.

How Can You Tell the Difference Between Flu and COVID-19?

Flu and COVID-19 are caused by different viruses, but they share many of the same symptoms, including fever, cough, sore throat, fatigue, and body aches. The flu often comes on suddenly, with pronounced body aches and fatigue, while COVID-19 symptoms may develop more gradually and can sometimes include a loss of taste or smell. COVID-19 can also cause lingering symptoms, known as Long COVID.

However, symptoms alone can’t reliably tell you which illness you have. Testing for flu and COVID-19 is the best way to identify the virus and help determine the appropriate treatment.

Full Symptom Comparison: Flu vs. COVID-19 vs. RSV

Symptom / Feature	Flu	COVID-19	RSV
Onset	Sudden, often overnight	Gradual, over a few days	Gradual, over 1–2 days
Fever	Common, often high (103–104°F)	Common, variable	Sometimes, often absent in infants
Cough	Common	Common	Common
Sore throat	Common	Common	Uncommon
Runny/stuffy nose	Sometimes	Sometimes	Common
Sneezing	Sometimes	Uncommon	Common
Body aches	Common, often severe	Sometimes	Sometimes
Fatigue	Common	Common	Sometimes
Headache	Common	Sometimes	Sometimes
Shortness of breath	Sometimes	Sometimes	Sometimes, wheezing in kids
Loss of taste/smell	Rare	Sometimes	Rare
Highest-risk groups	Kids under 5, adults 65+	Immunocompromised, chronic illness	Infants under 6 months, adults 60+

Quick Reference: The Fastest Ways to Tell Them Apart

• Sudden, “hit by a truck” onset with a very high fever? Lean flu.
• Lost your sense of taste or smell, or have lingering fatigue/brain fog after other symptoms fade? Lean COVID-19.
• A baby or toddler with wheezing, or an older adult with a chronic lung condition getting worse? Lean RSV.
• Not sure, or symptoms are getting worse instead of better? That’s when testing and a same-day visit make the difference.

When Each One Is Most Dangerous

Flu

The highest-risk for young children (especially under 2), adults 65 and older, pregnant women, and people with chronic conditions like asthma or diabetes. The CDC estimates that 6,000 to 27,000 children under 5 are hospitalized with flu-related complications each year. Complications can include pneumonia and worsening of existing heart or lung disease.

COVID-19

Carries the highest risk for people who are immunocompromised, have underlying heart, lung, or kidney disease, or are unvaccinated and in an older age group. It’s also the only one of the three known for causing lingering symptoms weeks after the initial illness.

RSV

The most dangerous for infants under 6 months (especially those born prematurely), young children with heart or lung conditions, and adults 60 and older with COPD, asthma, or heart failure.

Should You Get Tested?

Testing is especially worth doing if you’re in a high-risk group, if your symptoms are severe, or if you’re going to be around someone vulnerable (a newborn, an elderly relative, someone undergoing cancer treatment). Combination flu/COVID/RSV tests are available at many urgent care locations and can help your provider decide on treatment — including antivirals like oseltamivir (Tamiflu) for flu or Paxlovid for COVID-19, both of which work best when started within the first couple of days of symptoms.

Get Tested and Treated Today

If you’re not sure whether it’s flu, COVID-19, or RSV — or if symptoms are getting worse instead of better — don’t wait it out at home. ExperCARE offers walk-in visits with on-site rapid testing for flu, COVID-19, and RSV, so you can get an answer and a treatment plan the same day. Find your nearest ExperCARE location.

Prevention: What Actually Helps

• Annual flu vaccine, ideally by the end of October
• Updated COVID-19 vaccine, especially for those 65+ or with chronic conditions
• RSV vaccine for adults 60+ and pregnant women (to protect newborns), plus nirsevimab for eligible infants
• Frequent handwashing, staying home when sick, and improving indoor ventilation during peak season

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Frequently Asked Questions

Can you have the flu, COVID-19, and RSV at the same time?

It’s uncommon but possible to be co-infected with more than one respiratory virus at once, which can make symptoms more severe. This is one reason providers may test for all three at once.

Which one is more contagious — flu, COVID-19, or RSV?

COVID-19 is generally considered the most contagious of the three, though all spread easily through respiratory droplets, especially in indoor, close-contact settings like schools and daycares.

How soon after exposure do symptoms start for each?

Per CDC guidance, flu symptoms typically appear 1–4 days after exposure, COVID-19 symptoms 2–14 days (most commonly 3–5 days), and RSV symptoms 4–6 days after exposure.

Is a loss of smell always COVID-19?

Not always, but it’s a much more common and pronounced symptom with COVID-19 than with flu or RSV, making it one of the more useful distinguishing signs.

Do flu and COVID-19 vaccines protect against RSV?

No. Each virus requires its own vaccine. Per the CDC, RSV vaccines are approved for adults 60+ and for use during pregnancy; there is a separate preventive antibody (nirsevimab) for infants.

How long am I contagious with each virus?

Flu: about 5–7 days from symptom onset. COVID-19: typically 5–10 days, longer in some cases. RSV: 3–8 days, though infants and immunocompromised people can shed the virus for weeks.

Can kids get all three in one season?

Yes — reinfection and back-to-back infections with different viruses are common in school-age children, especially during peak fall and winter months.

What’s the difference between a cold and these three viruses?

A common cold usually causes milder symptoms — runny nose and mild cough — without the high fever, significant body aches, or breathing complications that flu, COVID-19, or RSV can cause.

Should I go to urgent care or the ER?

Urgent care is appropriate for testing, evaluation, and treatment of typical flu, COVID-19, or RSV symptoms. Go to the ER for difficulty breathing, chest pain, bluish lips, confusion, or symptoms that suddenly worsen.

How long should I stay home from work or school?

General guidance is to stay home until you’ve been fever-free for 24 hours without medication and symptoms are clearly improving, regardless of which of the three viruses you have.

Are at-home tests as accurate as the tests used at urgent care?

Not always. At-home tests look for proteins from the virus (antigen tests), and they work best when you have a lot of virus in your body. A positive result is reliable. A negative result doesn’t rule out an infection, especially early on, so you may still be sick. ExperCARE often uses molecular tests, which detect the virus’s genetic material and can pick up an infection earlier and more accurately. If you’re high-risk, symptoms are getting worse, or you’ll be around someone vulnerable, a test at ExperCARE can give you a more dependable answer.

 

The Bottom Line Flu, COVID-19, and RSV overlap enough that guessing isn’t reliable. But a few patterns can point you in the right direction: sudden, severe symptoms favor flu, lost taste or smell and lingering fatigue favor COVID-19, and wheezing in a baby or older adult favors RSV. When it matters — because you’re high-risk, symptoms are getting worse, or you need to know before seeing a vulnerable family member — same-day testing is the fastest way to get a clear answer and the right treatment. Need to get checked? Find your nearest ExperCARE and walk in any day of the week.