COVID-19 and common Flu are caused by different viruses, yet their symptoms often look very similar. Because of this, people become confused about what infection they or their family members may have. Knowing the difference can help in early isolation, proper treatment, and preventing unnecessary panic.
COVID-19
COVID-19 is caused by the SARS-CoV-2 virus. Although symptoms can vary from mild to severe, COVID-19 primarily affects the respiratory system. It can also impact other organs such as the heart, liver, and nervous system.
Flu (Influenza)
Flu is caused by influenza viruses mainly Type A and Type B. The flu spreads rapidly during the winter months and typically causes sudden onset symptoms such as fever, body ache, and fatigue. Unlike COVID, influenza rarely affects the body long-term after recovery.
Why COVID-19 and Flu Symptoms Are So Similar
Both viruses spread through droplets when an infected person coughs, sneezes, talks, or breathes. Both infect the respiratory system, which is why the symptoms overlap. The challenge is that COVID-19 can present with some unique signs not commonly seen in flu patients.
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| Image: The New York Times |
Key Differences in COVID-19 vs Flu Symptoms
| Symptom | COVID-19 | Flu |
|---|---|---|
| Fever | Often mild or moderate | Usually high and sudden |
| Cough | Persistent, dry | Mild to moderate |
| Loss of smell/taste | Common | Rare |
| Body aches | Mild to severe | Severe |
| Sore throat | Common | Very common |
| Breathing difficulty | More common | Less common |
| Fatigue | Long-lasting | 5–7 days |
| Runny nose | Sometimes | Common |
| Stomach issues | More common | Rare |
| Onset | Gradual | Sudden |
A. Fever
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COVID-19: Fever may appear mild or moderate and may come and go. Some COVID patients do not experience fever at all.
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Flu: Fever is usually high (above 100°F/38°C) and sudden in onset.
B. Cough
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COVID-19: Dry cough is one of the hallmark symptoms. Persistent coughing may last for weeks.
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Flu: Cough is usually mild to moderate and improves within a week.
C. Loss of Taste and Smell
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COVID-19: Sudden loss of smell (anosmia) and taste is a unique symptom that strongly indicates COVID infection.
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Flu: Rare. Flu generally does not cause complete loss of taste or smell.
D. Breathing Difficulty
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COVID-19: Shortness of breath, chest tightness, and difficulty breathing appear in moderate to severe cases.
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Flu: Seen mostly in elderly or those with chronic diseases; less common than in COVID.
E. Fatigue
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COVID-19: Fatigue is persistent and can last weeks or months (post-COVID fatigue).
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Flu: Tiredness is strong but usually lasts 5–7 days.
F. Sore Throat
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COVID-19: Sore throat is common but not universal.
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Flu: Sore throat is more common in flu patients than COVID patients.
G. Runny or Blocked Nose
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COVID-19: Mild nasal congestion or runny nose can occur.
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Flu: More frequent in flu infections.
H. Body Ache
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COVID-19: Body ache can be moderate to severe and long-lasting.
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Flu: One of the strongest symptoms patients often feel extreme body ache.
I. Gastrointestinal Symptoms
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COVID-19: Diarrhea, nausea, stomach pain can occur in many cases.
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Flu: GI symptoms are less common, usually seen in children.
Symptom Onset: Sudden vs Gradual
One of the easiest ways to distinguish flu from COVID-19 is by observing how fast symptoms appear.
COVID-19: Gradual Onset
Symptoms usually appear slowly over 2–14 days after exposure. You may start with mild fatigue, slight cough, or sore throat.
Flu: Sudden Onset
Symptoms begin rapidly often within a few hours. Many patients say, “I suddenly felt sick.”
Duration of Symptoms
COVID-19
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Symptoms may last 10–14 days.
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Some experience long-COVID symptoms for weeks or months.
Flu
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Usually resolves within 5–7 days.
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Weakness can remain for 1–2 weeks.
COVID-19 Symptoms That Are Not Common in Flu
These symptoms strongly indicate COVID infection:
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Loss of smell and taste
Prolonged cough lasting more than two weeks
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Severe chest discomfort and breathlessness
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Unusual skin rashes (COVID skin manifestations)
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Brain fog or difficulty concentrating
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Long-lasting fatigue even after recovery
Flu Symptoms That Are Less Common in COVID-19
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Very high fever with chills
Extreme body pain suddenly
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Frequent sneezing
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Shorter duration of illness
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Strong sore throat and runny nose
Who Is at Higher Risk?
COVID-19 High-Risk Groups
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Elderly (60+ years)
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People with diabetes, hypertension, asthma, or kidney disease
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Obese individuals
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People with weak immunity
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Pregnant women
Flu High-Risk Groups
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Children under 5 years
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Adults over 65
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Pregnant women
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People with chronic respiratory illness
How Testing Helps?
Types of COVID-19 Tests
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RT-PCR: Most accurate test.
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Rapid antigen test: Quick results but less accurate.
Types of Flu Tests
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Rapid influenza diagnostic test (RIDT)
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RT-PCR for influenza
Frequently Asked Questions (FAQ)
1. How can I tell if I have COVID-19 or the flu?
COVID-19 and flu symptoms can be very similar, but certain clues help differentiate them. COVID often causes loss of smell and taste, gradual onset of symptoms, and longer-lasting fatigue. Flu usually begins suddenly with high fever and severe body ache. However, testing is the only accurate way to confirm.
2. Is loss of smell a definite sign of COVID-19?
Yes. While not 100% of COVID cases have this symptom, sudden loss of smell or taste is far more common in COVID-19 than in flu. It is considered one of the strongest indicators of COVID infection.
3. Can the flu cause breathing difficulty like COVID-19?
Flu can cause breathing issues in severe cases, especially in people with lung diseases or weakened immunity. But COVID-19 is known to cause more frequent and more serious breathing problems, including low oxygen levels.
4. Which one spreads faster, COVID or flu?
Both spread through droplets from coughing, sneezing, or talking. However, COVID-19 has a higher transmission rate, especially with newer variants. It can spread even from people with no symptoms, making it more contagious than seasonal flu.
5. Can I have COVID-19 and flu at the same time?
Yes. Co-infection is possible. If symptoms are severe or unusual, you should get both COVID-19 and influenza tests. Dual infections may require more careful monitoring.
6. Do vaccines protect against both flu and COVID-19?
No. COVID-19 vaccines protect against the coronavirus, while flu vaccines protect against influenza viruses. You can take both vaccines—they do not interfere with each other and offer stronger overall protection.
7. How long do COVID-19 symptoms last compared to flu symptoms?
Flu symptoms typically last 5–7 days. COVID-19 symptoms can last 10–14 days or even longer. Some people experience long-COVID symptoms such as fatigue, cough, and weakness for several weeks or months.
8. When should I see a doctor for COVID or flu symptoms?
Seek medical care immediately if you experience:
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Difficulty breathing
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Chest pain
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Persistent high fever
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Oxygen saturation below 94%
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Severe vomiting or dehydration
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Confusion or fainting
9. Can home remedies cure COVID-19 or flu?
Home remedies such as rest, hydration, warm fluids, and steam inhalation can help relieve symptoms, but they do not cure COVID or flu. For severe or persistent symptoms, medical treatment is necessary.
10. What is the best way to prevent both COVID-19 and flu?
The best preventive measures include vaccination, wearing masks in crowded places, washing hands frequently, maintaining physical distance, and staying home when sick.
More:
1. AAP and CDC Clash Over COVID-19 Vaccines for Young Children
2. JN 1 COVID Symptoms, preventive measures & Cases in India
3. Dr Maria talks about the current surge in respiratory diseases and COVID JN.1 subvariant