Flu vs. COVID-19: Key Differences in Symptoms
Influenza and COVID-19 share many symptoms but have critical differences. Compare symptom profiles, incubation periods, contagiousness, severity, and when to get tested.
Medically reviewed by
Dr. Sarah Mitchell, MD
Influenza and COVID-19 are both contagious respiratory illnesses, but they're caused by different viruses. Because they share many symptoms, testing is often the only way to confirm which one you have. Here's what you need to know.[1][2]
Symptom Comparison
| Symptom | Influenza | COVID-19 |
|---|---|---|
| Fever / Chills | Very common | Common |
| Cough | Common (dry) | Common (dry) |
| Shortness of breath | Sometimes | More common |
| Fatigue | Very common | Very common |
| Body aches | Very common, severe | Common |
| Headache | Common | Common |
| Loss of taste/smell | Rare | More distinctive of COVID-19 |
| Sore throat | Common | Common |
| Runny nose | Sometimes | Common |
| Nausea/Vomiting | Sometimes (more in children) | Sometimes |
| Diarrhea | Sometimes (more in children) | Sometimes |
Sources: CDC Flu vs. COVID-19, WHO Q&A
Key Differences
⏱️ Symptom Onset
- Flu: Typically sudden — 1-4 days after exposure. You go from fine to very sick in hours[1]
- COVID-19: More gradual — 2-14 days after exposure (average ~5 days). Symptoms may build over several days[2][3]
👃 Loss of Smell/Taste
While both can cause loss of smell or taste, it remains more distinctive of COVID-19. With the flu, nasal congestion can reduce smell, but the sudden, complete loss without congestion is more typical of COVID-19.[1][4]
🫁 Breathing Problems
Shortness of breath is more common and often more severe with COVID-19.While severe flu can cause breathing difficulty (especially if pneumonia develops), COVID-19 is more likely to cause persistent shortness of breath even without pneumonia.[1][5]
📊 Severity & Complications
- COVID-19: Higher risk of severe outcomes, including blood clots, multi-organ effects, and Long COVID[3]
- Flu: Can also be severe, especially in high-risk groups, but post-viral complications are generally shorter-lived[1]
Can You Have Both?
Yes — co-infection with influenza and COVID-19 is possible. This is sometimes called "flurona." Co-infection can result in more severe illness. Testing is the only reliable way to know.[2][4]
⚠️ What To Do
If you have symptoms of either illness:
- Get tested — COVID-19 and flu tests are widely available. Combination tests exist[2]
- Isolate — Both are highly contagious[1]
- Contact your doctor — Antivirals exist for both (Tamiflu for flu, Paxlovid for COVID-19) and work best when started early[3]
- Monitor for emergency signs — Difficulty breathing, persistent chest pain, confusion, bluish lips[5]
References
- CDC. "Similarities and Differences between Flu and COVID-19." Centers for Disease Control and Prevention. cdc.gov/flu/symptoms/flu-vs-covid19.htm
- WHO. "Coronavirus disease (COVID-19): Similarities and differences with influenza." World Health Organization.
- NHS. "COVID-19 Symptoms and What to Do." National Health Service. nhs.uk/conditions/covid-19/
- Mayo Clinic. "COVID-19, cold, allergies and the flu: What are the differences?" mayoclinic.org
- Cleveland Clinic. "Influenza (Flu)." my.clevelandclinic.org
Sources
This article references information from the CDC, WHO, NHS, and peer-reviewed medical literature. Content is reviewed regularly for accuracy. Learn about our editorial policy.