Flu, COVID-19 and Colds

Three viruses with a lot of overlap. You often can’t tell them apart by symptoms alone, but a test can, and that matters if you’re at higher risk because antivirals work best early.

Quick answer: Colds come on slowly with a runny nose. Flu hits suddenly with fever, aches and exhaustion. COVID-19 can look like either. A rapid antigen test or PCR swab tells them apart. If you’re older or at higher risk, test early: flu antivirals work best within 48 hours, COVID antivirals within 5 days of symptoms.

Telling them apart

• Common cold: comes on over a day or two; runny or blocked nose, sneezing and a sore throat; fever is rare in adults. Usually better in 7 to 10 days. See common cold.
• Flu (influenza): starts suddenly, often within hours, 1 to 4 days after exposure. Fever, chills, body aches, headache, dry cough and exhaustion. Worst for 3 to 5 days; tiredness and cough can last 2 weeks or more.
• COVID-19: anything from no symptoms to severe illness, usually starting 2 to 5 days after exposure (up to 14). Sore throat, cough, fever, tiredness, runny nose and headache are common; loss of smell or taste is less common than earlier in the pandemic.
• RSV and other viruses cause similar symptoms and can be severe in babies and older adults.

Our cold vs flu comparison goes symptom by symptom.

Testing

• Rapid antigen tests (RATs): combined tests for COVID-19 and flu A and B are sold in pharmacies. A positive result is reliable. A negative result early on doesn’t rule infection out, so if you still have symptoms, test again 24 to 48 hours later.
• PCR swabs through your GP or a clinic are more accurate and can test for several viruses at once.
• Why test: if you’re at higher risk of severe illness, a positive test can get you antivirals in time. It also helps you protect vulnerable people around you.

Antivirals: who qualifies

Antivirals don’t replace vaccines. They lower the risk of severe illness in people at higher risk, and work best when started early.

1. Flu · PrescriptionOseltamivirCapsules or liquid, twice a day for 5 days. Zanamivir (inhaled) and baloxavir (a single dose) are alternatives in some countries.

   Who

   Anyone in hospital with flu, and people at higher risk: adults 65 and over, children under 5, pregnant women, people with heart, lung, kidney or liver disease, diabetes, a weakened immune system or severe obesity, First Nations people, and aged care residents

   When

   Ideally within 48 hours of symptoms; still considered later for people who are very unwell

   Works

   In healthy adults, symptoms ease about 17 hours sooner on average (Cochrane 2014); the bigger benefit is for people at higher risk

   Watch for

   Nausea and vomiting; take with food.

2. COVID-19 · PrescriptionNirmatrelvir with ritonavirTablets twice a day for 5 days. Molnupiravir is an alternative in some countries when this can’t be used.

   Who

   People at higher risk of severe COVID-19. In Australia it’s PBS-subsidised for everyone 70 and over, people 50 and over with 2 risk factors, First Nations adults 30 and over with 1 risk factor, adults with a moderately to severely weakened immune system, and adults previously in hospital with COVID-19

   When

   Within 5 days of symptoms starting

   Works

   Lowers the chance of hospital admission in people at higher risk

   Watch for

   Ritonavir interacts with many medicines, including some statins, blood thinners and heart medicines, so your doctor or pharmacist must check all of yours. A bitter taste is common.

If you’re likely to qualify, make a plan with your GP before winter so you can get a script quickly, including by telehealth.

Self-care

• Rest, drink plenty, and use paracetamol or ibuprofen for fever and aches if needed.
• Antibiotics don’t work on viruses. They only help if a bacterial infection develops, such as some pneumonias.
• Stay home while you’re unwell, and wear a mask if you must go out or are near vulnerable people.
• Cough into your elbow and wash your hands often.

Vaccines

• Flu: everyone 6 months and over is recommended a flu vaccine every year, because the circulating strains change. In Australia it’s free under the National Immunisation Program for children 6 months to under 5, pregnant women (each pregnancy), Aboriginal and Torres Strait Islander people from 6 months, people 65 and over, and people with certain medical conditions. Have it from April, before the winter peak.
• COVID-19 (Australia, on the National Immunisation Program from 1 October 2026): adults 75 and over, 2 doses a year; adults 65 to 74, 1 dose a year; Aboriginal and Torres Strait Islander adults 50 to 74, 1 dose a year; adults 18 to 64 with a severely weakened immune system, 1 dose a year. Other adults can consider a yearly dose, and pregnant women can consider one from 20 weeks; these aren’t funded.
• Flu and COVID-19 vaccines can be given at the same visit.
• RSV vaccines are now offered in pregnancy and to older adults in many countries, including Australia. Ask your GP whether you qualify.

See your GP if

• You’re at higher risk and test positive, or have flu-like symptoms: call early, within the first day or two
• You’re getting worse after 3 to 5 days, or start to improve and then get worse again
• You have a cough that lasts more than 3 weeks, or breathlessness that lingers
• Symptoms last more than 3 months after COVID-19 (long COVID)

Call 000 (Australia) or your local emergency number for difficulty breathing or breathlessness at rest, chest pain or pressure, blue or grey lips, confusion or being hard to wake, fainting, a seizure, or not passing urine. In children, also: fast breathing or sucking in under the ribs, floppiness, not drinking, or a rash that doesn’t fade when pressed.

Health days. World Immunization Week is in late April, and the International Day of Epidemic Preparedness is on 27 December: see our health days calendar.

Evidence and more information

• WHO: Influenza (seasonal) fact sheet
• Jefferson et al, Cochrane 2014: Neuraminidase inhibitors for influenza
• CDC: Similarities and differences between flu and COVID-19
• ATAGI 2026: Transition of COVID-19 vaccines to the National Immunisation Program
• PBS factsheet: Nirmatrelvir and ritonavir eligibility (December 2024)
• healthdirect: Flu

Updated 8 November 2026. General education, not personal medical advice. Talk to your GP or pharmacist about your situation.

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