Cold, flu or COVID-19: how to tell them apart — and when to get care
A blocked nose, a fever, a cough that will not quit. Every cold-and-flu season, Australians ask the same question: which virus do I have, and does it need a doctor?
Book a telehealth GP from $49 Cold, flu & COVID treatment infoThe short answer
All three illnesses are caused by respiratory viruses, and their symptoms overlap so much that even GPs cannot reliably tell them apart without a test. But there are useful patterns:
🤧 Cold
Usually mild. Sneezing, runny nose and a scratchy throat. You feel ordinary-unwell, not flattened. No fever in most adults.
🤒 Flu
Hits hard and fast. Sudden fever, chills, body aches and exhaustion that knock you flat for days. Vaccination reduces severity.
🦠 COVID-19
The wildcard. Can mimic a mild cold, look exactly like flu, or cause serious illness — especially in older or higher-risk people.
Symptom comparison at a glance
| Symptom | Cold | Flu | COVID-19 |
|---|---|---|---|
| Fever | Rare | Common, sudden (38°C+) | Common |
| Body aches | Mild | Common, often severe | Common |
| Fatigue | Mild | Severe, can last weeks | Often significant |
| Sneezing / runny nose | Very common | Sometimes | Sometimes |
| Sore throat | Very common | Sometimes | Common |
| Cough | Mild to moderate | Common, dry | Common, dry |
| Headache | Rare | Common | Common |
| Shortness of breath | Rare | Uncommon | Can occur; more likely with severe illness |
| Loss of taste or smell | Rare | Rare | Possible |
| Onset | Gradual | Sudden | Varies |
| Typical duration | 7–10 days | 1–2 weeks | Varies; most recover in days to weeks |
What each illness typically feels like
Cold — gradual and mild
Colds are caused by hundreds of viruses, most commonly rhinoviruses. Symptoms build over a day or two: sneezing, a runny or blocked nose, a scratchy throat and a mild cough. Antibiotics do not help — colds are viral, and most people recover in 7–10 days with rest and simple pharmacy remedies.
Flu — sudden and severe
Influenza comes on fast — many people say they were fine at lunch and terrible by dinner. Expect fever and chills, muscle and joint aches, severe tiredness, headache and a dry cough. It usually keeps you in bed for 3–5 days, with full recovery taking 1–2 weeks. For higher-risk groups — adults over 65, pregnant women, young children, Aboriginal and Torres Strait Islander people, and anyone with asthma, heart disease, diabetes or other chronic conditions — flu can become serious, including pneumonia.
COVID-19 — the mimic
Today's variants often start with a sore throat, followed by congestion, sneezing, a dry cough, fatigue, headache and sometimes fever. Some people also get nausea or diarrhoea. Because it mimics the others so closely, testing matters: if a RAT is negative but you still feel unwell, test again 24–48 hours later — early tests can miss infection.
When to see a doctor
You do not need to drag yourself to a clinic for most respiratory illnesses. A telehealth GP can assess your symptoms, arrange testing or treatment, and issue prescriptions and medical certificates without you leaving the couch.
See a GP (telehealth is usually enough) if:
- Symptoms are severe, worsening, or lasting more than about 10 days
- You are in a higher-risk group — over 65, pregnant, immunocompromised, or living with asthma, lung disease, heart disease, diabetes or kidney disease
- You have a fever above 38.5°C that will not settle, or keeps returning
- You improve, then suddenly get worse — this can signal a secondary infection such as a chest infection or sinusitis
- You may need antivirals — flu antivirals work best within 48 hours of symptoms starting, and COVID-19 antivirals are available for eligible higher-risk people
- You need a medical certificate for work or study
How a telehealth GP helps
- Book online, rest at home Book a video or phone consultation and stay in bed — you avoid spreading the virus in a waiting room. Consultations start from $49, and if telehealth is not clinically appropriate, the doctor will tell you and guide you to in-person care.
- Get assessed and tested The GP reviews your symptoms, history and risk factors, helps interpret your RAT result in context, and can arrange PCR testing, pathology or imaging referrals where needed.
- Receive treatment and documents Where clinically appropriate, prescriptions (including antivirals) are sent straight to your pharmacy from $25, and a medical certificate for work or study can be issued from $15 — often within the same consultation.
🚨 Call 000 or go to your nearest emergency department if you have:
- Difficulty breathing or shortness of breath at rest
- Chest pain or pressure
- Confusion, fainting or severe dizziness
- Blue or grey lips, face or skin
- A fever with a stiff neck, or a rash that does not fade when pressed
- In babies and young children: floppiness, unresponsiveness, refusing fluids, or far fewer wet nappies than usual
If in doubt, call triple zero (000) — it is always better to over-react than to wait.
Recovering at home: what actually helps
- Rest — your immune system does its best work while you sleep
- Fluids — water, warm drinks and soup; aim for pale-yellow urine
- Paracetamol or ibuprofen for fever and aches, taken as the label directs
- Stay home while feverish, and wear a mask around others if you must go out
- Ventilate — opening windows and doors reduces how easily viruses spread indoors
Ease back into work and exercise gradually. Pushing through fatigue — especially after flu or COVID-19 — tends to prolong recovery rather than speed it up.
How long am I contagious?
- Cold: most contagious in the first 2–3 days; generally fine after a week
- Flu: contagious from about a day before symptoms until 5–7 days after they start
- COVID-19: most contagious just before and during the first few days of symptoms; many people are no longer significantly infectious by 5 days, though some shed virus longer
Frequently asked questions
How can I tell the difference between a cold, flu and COVID-19 without a test?
You often cannot — the symptoms overlap heavily. Colds favour sneezing and a runny nose without much fever; flu hits suddenly with fever, aches and exhaustion; COVID-19 can look like either. A rapid antigen test is the only reliable way to confirm COVID-19 at home.
Should I retest if my COVID-19 RAT is negative but I feel unwell?
Yes. A single early negative can miss infection, so retest in 24–48 hours if symptoms persist. A GP can also arrange more sensitive PCR testing, which matters most if you are at higher risk of severe illness.
Can a telehealth doctor prescribe antivirals for flu or COVID-19?
Yes. Australian GPs can prescribe antivirals via telehealth when clinically appropriate. Timing matters — flu antivirals work best within 48 hours of symptoms starting, and COVID-19 antivirals are for eligible higher-risk people — so book early in your illness.
When should I go to hospital instead of seeing a GP?
Call 000 or go to an emergency department for breathing difficulty, chest pain or pressure, confusion, blue lips, severe dizziness or fainting. In children, watch for refusing fluids, floppiness or far fewer wet nappies than usual.
Can I get a sick certificate online if I have flu or COVID-19?
Yes. A telehealth GP can assess you by video or phone and email a medical certificate, often within the same consultation. Certificates start from $15, and repeat prescriptions are available from $25 if you need ongoing medication.
Medically reviewed by Dr John Youssef, MBBS, FRACGP
Last reviewed: October 2026
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