Medical

Understanding the Differences: Flu, RSV, COVID-19 and Whooping Cough

6th May 2026

The four of the most common respiratory illness can look alike but they are caused by different viruses and tend to affect people in different ways. This article breaks down the key differences and what to look out for.

Every year in Australia, a mix of respiratory illnesses circulates through homes, workplaces, schools and childcare centres. Many of them cause similar symptoms, including coughs, fevers, runny noses and fatigue which can make them hard to tell apart.

Four of the most common are the Flu, RSV, COVID 19 and Whooping Cough. Even though they can look alike, they are caused by different viruses and tend to affect people in different ways.

This article helps break down the key differences using information from Australian government and authorised medical sources. It is general information only and does not offer health advice.

What Each Illness Actually Is

Flu (Influenza)

Influenza is caused by Influenza A and B viruses. It tends to come on suddenly, with fever, aches and exhaustion. In Australia, flu activity usually peaks during the cooler months.

RSV (Respiratory Syncytial Virus)

RSV is a virus that is especially common in young children. It is one of the main causes of bronchiolitis and pneumonia in infants but it also affects adults, particularly older people.

COVID-19

COVID-19 is caused by the SARS CoV 2 coronavirus. It can range from no symptoms at all to severe pneumonia. Some people experience longer lasting symptoms after the initial infection.

Whooping Cough (Pertussis)

Whooping Cough is caused by the Bordetella pertussis bacterium. It’s known for long lasting coughing fits that can be severe, especially in babies. Some people make a “whoop” sound when breathing in after a coughing burst.

How They Spread

All four illnesses spread mainly through respiratory particles that are released when someone breathes, talks, coughs or sneezes.

Flu: spreads through droplets and contaminated surfaces, especially indoors.
RSV: spreads through droplets and shared surfaces. Childcare centres often see waves of RSV.
COVID-19: spreads through respiratory particles in the air, particularly in indoor or poorly ventilated spaces.
Whooping Cough: spreads easily through close contact.

Common Symptoms

Symptoms overlap a lot, which is why health authorities emphasise that medical testing is how these infections are distinguished.

Flu: Often begins suddenly with fever, chills, muscle aches, headache and fatigue.
RSV: Runny nose, cough and fever are common. In babies, RSV can cause wheezing or difficulty feeding due to breathing effort.
COVID-19: Symptoms vary widely but could include ever, cough, sore throat, runny nose and tiredness are common. Loss of taste or smell can occur in some cases.
Whooping Cough: Starts like a mild cold, then progresses to intense coughing fits that can last for weeks.

Who Is Most Affected

Australian health departments highlight certain groups as more likely to experience severe illness:

Flu: young children, older adults, pregnant people and those with chronic conditions
RSV: infants (especially under 12 months) and older adults
COVID-19: older adults, people with chronic conditions and other groups identified in national guidelines
Whooping Cough: young infants

How Authorities Track and Diagnose These Infections

Testing: PCR tests and respiratory panels are used to confirm which virus or bacterium is responsible. Rapid antigen tests are widely used for COVID 19 and sometimes for flu.
Surveillance: The Australian Government publishes weekly respiratory surveillance reports tracking flu, RSV and COVID 19 activity across the country.
Vaccination and Public Health Measures (Described, Not Advised)
Australian health departments publish information on vaccines and other population level strategies:
Vaccines exist for flu, COVID 19, and whooping cough.
RSV immunisation options (such as maternal vaccination and monoclonal antibodies for infants and older adults) are available in Australia.
Public health messaging often highlights measures such as staying home when unwell, hand hygiene, masks in certain settings and improving ventilation, described as ways to reduce community spread.

At a glance

This summary highlights the key differences between common respiratory illnesses at a glance:

If you are experiencing symptoms such as fever, cough, or other signs of a respiratory illness, we encourage you to visit one of our centres to see a GP. To help protect other patients and our teams, we also ask that you follow good social etiquette, including wearing a mask where appropriate.