Flu vs. COVID-19 vs. RSV: How to Tell the Difference

An Evidence-Based Guide from Emcura Medical Clinic

By a Board-Certified Family & Integrative Medicine Physician

Fever, cough, congestion, sore throat, fatigue, and body aches can all signal a respiratory infection—but is it influenza (flu), COVID-19, or RSV?

These three viral illnesses share many symptoms, making it difficult to know which infection you have based on symptoms alone. While most healthy people recover with supportive care, each virus can cause serious illness in certain individuals, and early diagnosis may affect treatment decisions.

At Emcura Medical Clinic, we evaluate respiratory illnesses every day. Our goal is to identify the likely cause of your symptoms, determine when testing or antiviral treatment may be appropriate, and recognize warning signs that require a higher level of care.

What Are Flu, COVID-19, and RSV?

All three are contagious respiratory illnesses caused by viruses, but they are caused by different viruses.

Influenza is caused primarily by influenza A and B viruses.

COVID-19 is caused by the SARS-CoV-2 virus.

RSV, or respiratory syncytial virus, is another common respiratory virus. Nearly everyone is infected with RSV at some point, but it can be particularly serious for infants, older adults, and people with certain underlying health conditions.

Because symptoms overlap considerably, testing may be the best way to distinguish between them when knowing the specific virus would affect treatment or precautions.

Flu vs. COVID-19 vs. RSV: Common Symptoms

There is enough overlap that this table should be used as a general guide—not as a way to diagnose yourself.

What Does the Flu Usually Feel Like?

Influenza often comes on quickly.

Many patients can remember when they suddenly began feeling sick.

Common flu symptoms include:

• Fever

• Chills

• Significant body aches

• Headache

• Fatigue

• Dry cough

• Sore throat

• Nasal congestion

• Reduced appetite

Some children may also experience vomiting or diarrhea.

One feature that often distinguishes influenza from a mild cold is the intensity of symptoms. Patients frequently describe feeling relatively well one day and significantly ill the next.

What Does COVID-19 Usually Feel Like?

COVID-19 symptoms vary considerably from person to person and between circulating variants.

Common symptoms may include:

• Sore throat

• Cough

• Nasal congestion

• Runny nose

• Fever

• Chills

• Fatigue

• Headache

• Muscle aches

• Shortness of breath

• Nausea or diarrhea

Loss of taste or smell can still occur, although it is not as consistently reported as it was earlier in the pandemic.

Because COVID-19 can look very similar to influenza or a common cold, symptoms alone cannot reliably confirm or exclude COVID-19.

What Does RSV Usually Feel Like?

In healthy adults and older children, RSV often resembles a common cold.

Symptoms may include:

• Runny nose

• Nasal congestion

• Cough

• Sneezing

• Reduced appetite

• Fever

• Wheezing

For most healthy adults, symptoms remain relatively mild.

However, RSV can cause more serious lower respiratory tract disease, including bronchiolitis or pneumonia, particularly in infants, older adults, and people with certain chronic medical conditions.

Who Is Most at Risk From RSV?

RSV deserves particular attention in certain populations.

Higher-risk groups include:

• Young infants

• Premature infants

• Adults age 75 and older

• Adults ages 50–74 with certain risk factors

• People with chronic heart or lung disease

• People with weakened immune systems

• Residents of nursing homes or long-term care facilities

In infants, RSV may sometimes cause decreased activity, poor feeding, irritability, or breathing difficulty rather than classic cold symptoms.

Which Illness Causes the Worst Body Aches?

Significant muscle aches are classically associated with influenza, especially when symptoms begin abruptly.

COVID-19 can also cause substantial body aches.

RSV in healthy adults generally causes fewer systemic symptoms and more often resembles a cold, although this is not always the case.

Again, symptom severity alone cannot definitively identify the virus.

What About Fever?

Fever can occur with all three infections.

Flu commonly causes fever, but not everyone with influenza develops one.

COVID-19 may or may not cause fever.

RSV can also cause fever, particularly in children.

Therefore, the presence—or absence—of fever cannot reliably distinguish between these illnesses.

Which Virus Causes Wheezing?

RSV is particularly associated with wheezing and lower-airway inflammation, especially in young children.

However, wheezing can occur with other respiratory infections, particularly in patients with:

• Asthma

• COPD

• Reactive airway disease

• Previous respiratory problems

New or worsening wheezing should be evaluated, especially when accompanied by difficulty breathing.

Can You Have More Than One Virus at the Same Time?

Yes.

It is possible to be infected with more than one respiratory virus simultaneously.

For example, someone could have influenza and COVID-19 at the same time.

Coinfections are not the most common scenario, but they do occur and may be more concerning in higher-risk patients.

How Are Flu, COVID-19, and RSV Diagnosed?

Testing may include nasal or nasopharyngeal swabs.

Depending on the clinical setting, testing may evaluate for:

• Influenza A

• Influenza B

• COVID-19

• RSV

Some rapid molecular tests can check for multiple respiratory viruses from a single sample.

Your provider can determine whether testing is likely to change treatment or management.

When Is Testing Most Helpful?

Testing can be particularly useful when:

• Symptoms are moderate or severe.

• You are at higher risk for complications.

• Antiviral treatment is being considered.

• You have had a known exposure.

• You live with someone who is medically vulnerable.

• Your symptoms are worsening.

• Knowing the diagnosis would affect work, school, travel, or infection-control decisions.

Is There Treatment for Influenza?

Yes.

Prescription antiviral medications may reduce the severity and duration of influenza and are particularly important for people at higher risk of complications.

Examples include:

• Oseltamivir

• Baloxavir

• Zanamivir in selected patients

Flu antivirals generally provide the greatest benefit when started as early as possible, ideally within 48 hours of symptom onset, although treatment may still be recommended later for hospitalized, severely ill, or higher-risk patients.

Is There Treatment for COVID-19?

Yes.

Antiviral treatment may be appropriate for patients at increased risk of developing severe COVID-19.

Treatment options may include medications such as nirmatrelvir/ritonavir (Paxlovid) when medically appropriate.

Because some COVID-19 treatments must be started within a limited time after symptoms begin, higher-risk patients should contact a healthcare provider early in the illness.

Paxlovid can interact with numerous medications, so a medication review is important before prescribing it.

Is There Treatment for RSV?

For most people, RSV treatment is primarily supportive.

Treatment may include:

• Rest

• Hydration

• Fever management

• Nasal saline

• Monitoring breathing

There is not a routinely prescribed outpatient antiviral treatment for uncomplicated RSV comparable to common flu or COVID-19 antivirals.

Patients who develop significant breathing problems, dehydration, or low oxygen levels may require hospital-based treatment.

Do Antibiotics Treat Flu, COVID-19, or RSV?

No.

All three illnesses are caused by viruses, and antibiotics do not treat viral infections.

Antibiotics may be appropriate only if a secondary bacterial infection develops, such as certain cases of:

• Pneumonia

• Sinusitis

• Ear infection

Unnecessary antibiotic use can cause side effects and contribute to antibiotic resistance.

What Can You Do at Home?

Most uncomplicated respiratory infections improve with supportive care.

Helpful measures include:

• Rest

• Drinking plenty of fluids

• Warm liquids

• Honey for cough in adults and children older than one year

• Acetaminophen or ibuprofen when appropriate

• Saline nasal spray

• Humidified air

• Adequate sleep

Over-the-counter cold and cough medications should be selected carefully, particularly for young children and people with high blood pressure or other medical conditions.

How Long Do Symptoms Last?

Duration varies by virus and individual.

Influenza: Many uncomplicated symptoms improve within several days, although cough and fatigue may last longer.

COVID-19: Symptoms may last several days to weeks. A smaller number of patients develop persistent symptoms lasting considerably longer.

RSV: Most mild infections improve within approximately one to two weeks, although cough may linger.

Worsening symptoms after initial improvement deserve medical evaluation because they can sometimes indicate a complication or secondary infection.

When Should You Visit Urgent Care?

Consider an evaluation if you have:

• Persistent fever

• Significant sore throat

• Worsening cough

• Wheezing

• Dehydration

• Persistent vomiting

• Ear pain

• Sinus pain

• Symptoms that are not improving

• Concern about influenza, COVID-19, or RSV

• A medical condition that increases your risk of complications

Higher-risk patients should consider contacting a healthcare provider early because antiviral treatment may be time-sensitive.

When Should You Go to the Emergency Room?

Seek emergency medical care for:

• Significant difficulty breathing

• Severe or persistent chest pain

• Blue, gray, or unusually pale lips or skin

• New confusion

• Difficulty waking or staying awake

• Severe dehydration

• Fainting

• Rapid deterioration

• Other severe or concerning symptoms

For infants, seek prompt medical attention for breathing difficulty, poor feeding, unusual lethargy, dehydration, or concerning changes in behavior.

Can Flu, COVID-19, and RSV Be Prevented?

Prevention remains important, particularly for people at higher risk of severe respiratory illness.

Helpful measures include:

• Frequent handwashing

• Avoiding close contact with others when sick

• Improving indoor ventilation

• Covering coughs and sneezes

• Avoiding sharing drinks and utensils

• Staying current with recommended vaccinations

Vaccines are available to help protect against influenza, COVID-19, and RSV in eligible populations. RSV prevention recommendations vary by age, pregnancy status, and individual risk factors.

How Emcura Can Help

At Emcura Medical Clinic, we evaluate respiratory illnesses in children and adults and help determine whether symptoms are most consistent with influenza, COVID-19, RSV, or another condition.

Depending on your symptoms and risk factors, your evaluation may include:

• Medical history

• Physical examination

• Flu testing

• COVID-19 testing

• RSV testing when appropriate

• Oxygen level measurement

• Lung examination

• Evaluation for pneumonia or other complications

• Antiviral treatment when indicated

• Supportive treatment recommendations

• Referral for higher-level care when necessary

Our goal is to help you understand what is causing your symptoms and receive the right treatment without unnecessary medications.

The Bottom Line

Flu, COVID-19, and RSV can look remarkably similar.

Influenza often causes a sudden onset of fever, chills, significant body aches, headache, and fatigue. COVID-19 can cause a wide range of respiratory and systemic symptoms. RSV frequently resembles a cold in healthy adults but can cause serious respiratory illness in infants, older adults, and other vulnerable individuals.

Because symptoms overlap, testing may be necessary to know which virus is causing your illness—particularly when the diagnosis could affect antiviral treatment or other medical decisions.

At Emcura Medical Clinic, our providers can evaluate your symptoms, perform appropriate respiratory testing, identify complications, and help you get the treatment you need to recover safely.

References

1. Centers for Disease Control and Prevention. Signs and Symptoms of Flu.

2. Centers for Disease Control and Prevention. Symptoms of COVID-19.

3. Centers for Disease Control and Prevention. Respiratory Syncytial Virus (RSV).

4. Centers for Disease Control and Prevention. Clinical Guidance for Influenza Antiviral Medications.

5. National Institutes of Health. COVID-19 Treatment Guidelines.

6. Infectious Diseases Society of America. Guidelines on the Treatment and Management of Patients with COVID-19.

7. American Academy of Pediatrics. Respiratory Syncytial Virus.

8. Centers for Disease Control and Prevention. RSV Immunization Guidance.

Medical Disclaimer: This article is for educational purposes and does not replace personalized medical advice. Seek immediate medical care for difficulty breathing, severe chest pain, confusion, significant dehydration, blue or gray lips or skin, or other severe symptoms.