When you wake up with a sore throat, cough, congestion, or fever, it can be difficult to know what’s causing it. Many respiratory viruses share similar symptoms, especially in the first few days.

The four most common causes are:

• The common cold
• Influenza (flu)
• COVID-19
• RSV (Respiratory Syncytial Virus)

While symptoms often overlap, certain patterns can provide clues. However, testing is sometimes the only reliable way to know for sure.

Quick Comparison

Symptom	Common Cold	Flu	COVID-19	RSV
Fever	Rare or mild	Common	Common	Sometimes
Body aches	Mild	Often severe	Common	Mild to moderate
Fatigue	Mild	Significant	Common	Variable
Runny nose	Very common	Sometimes	Common	Very common
Sore throat	Common	Sometimes	Common	Common
Cough	Mild to moderate	Common	Common	Common
Shortness of breath	Rare	Sometimes	Sometimes	More common in high-risk groups
Loss of taste/smell	Rare	Rare	Can occur	Rare
Sudden onset	Usually gradual	Often sudden	Variable	Gradual

The Common Cold

The common cold is usually caused by viruses such as rhinoviruses.

Symptoms often include:

• Runny nose
• Sneezing
• Nasal congestion
• Mild sore throat
• Mild cough

Most colds:

• Develop gradually
• Cause little or no fever
• Improve within 7–10 days

People generally feel uncomfortable but can often continue normal activities.

Influenza (Flu)

Influenza is typically more intense than a cold.

Common symptoms include:

• Sudden fever
• Chills
• Severe body aches
• Significant fatigue
• Headache
• Dry cough

Many people can identify the flu because they feel as though they were “hit by a truck.”

Symptoms often begin abruptly over a few hours.

COVID-19

COVID-19 can resemble either a cold or the flu.

Common symptoms may include:

• Fever
• Cough
• Fatigue
• Congestion
• Sore throat
• Headache
• Muscle aches

Some people also experience:

• Loss or alteration of taste and smell
• Digestive symptoms
• Shortness of breath

Symptoms vary widely between individuals.

RSV

Respiratory Syncytial Virus Infection is often thought of as a childhood illness, but it can be serious in older adults.

Common symptoms include:

• Runny nose
• Cough
• Wheezing
• Congestion
• Fatigue

Adults may mistake RSV for a cold until symptoms worsen.

RSV can be particularly concerning for:

• Adults over 60
• People with lung disease
• People with heart disease
• Individuals with weakened immune systems

Symptom Clues That May Help

Likely a Cold

• Mostly nasal symptoms
• Mild fatigue
• Little or no fever
• Gradual onset

More Suggestive of Flu

• High fever
• Sudden onset
• Severe body aches
• Extreme fatigue

More Suggestive of COVID

• Combination of respiratory and systemic symptoms
• Loss of taste or smell
• Recent exposure to someone with COVID

More Suggestive of RSV

• Persistent cough
• Wheezing
• Significant congestion
• Symptoms in an older adult during RSV season

Can You Tell for Sure Based on Symptoms Alone?

Not always.

These infections can look remarkably similar.

For example:

• COVID can resemble a cold
• Flu can resemble COVID
• RSV can resemble both

Testing provides the most reliable answer when knowing the cause would affect treatment or precautions.

When Testing Is Most Helpful

Consider testing if:

• You have significant symptoms
• You are at high risk for complications
• You live with high-risk individuals
• You may qualify for antiviral treatment
• You need to make decisions about work, school, or travel

Who Is at Higher Risk for Complications?

People at increased risk include:

• Adults over 65
• Young children
• Pregnant individuals
• People with asthma
• People with chronic lung disease
• People with heart disease
• People with weakened immune systems

For these groups, early medical evaluation may be particularly important.

When Should You Call a Doctor?

Contact a healthcare professional if you develop:

• Difficulty breathing
• Chest pain
• Confusion
• Persistent high fever
• Severe dehydration
• Symptoms that are worsening rather than improving

These symptoms warrant prompt medical attention regardless of which virus is responsible.

What About Long-Term Symptoms?

Some viral illnesses can have lingering effects.

For example:

• Fatigue may persist after the flu
• Cough can linger after RSV
• Some individuals experience prolonged symptoms after COVID-19

Persistent symptoms should be discussed with a healthcare provider.

Prevention Matters

Several strategies help reduce risk:

Vaccination

Vaccines are available for:

• Influenza
• COVID-19
• Respiratory Syncytial Virus Infection (for certain age groups and risk categories)

General Prevention

• Wash hands regularly
• Stay home when sick
• Improve ventilation when possible
• Cover coughs and sneezes
• Maintain healthy sleep and nutrition habits

Bottom Line

The common cold, flu, COVID-19, and RSV can cause many of the same symptoms, making them difficult to distinguish based on symptoms alone. Colds usually cause milder nasal symptoms, flu often causes sudden fever and body aches, COVID can produce a wide range of respiratory and systemic symptoms, and RSV frequently causes significant cough and congestion, especially in older adults.

Because these infections overlap so much, testing may be needed to confirm the cause. If you develop severe symptoms such as breathing difficulties, chest pain, confusion, or signs of dehydration, seek medical care promptly regardless of which virus you think you have.