Flu, COVID-19 or a cold? How to tell the difference

September is approaching, but South Africans are still feeling the chill as the winter respiratory-virus season continues, with influenza still circulating.

But if you wake up with a cough, sore throat and blocked nose, how do you know whether it is flu, COVID-19 or simply a common cold? How do you know if you need to take that sick day (or three) or just take some citrus and a bit of medicine?  

As temperatures plunge across parts of South Africa, respiratory illnesses become more common.

The bigger problem is that the symptoms often overlap, making it difficult to know which virus is responsible without testing.

According to the National Institute for Communicable Diseases (NICD), South Africa’s 2026 influenza season began in the week of 9 March, which makes it the earliest start recorded since 2010 based on pneumonia surveillance data.

The NICD said A(H1N1)pdm09 was the most prevalent influenza A subtype in pneumonia surveillance and public clinics, while A(H3N2) was most prevalent in private general-practitioner surveillance.

According to the NICD’s latest Weekly Respiratory Pathogens Surveillance Report, 108 samples were tested, with 10 influenza cases (9.3%), 10 RSV cases (9.3%) and one SARS-CoV-2 case (0.9%) detected. The NICD says the influenza season has peaked, but the virus continues to circulate.

So, what should you look out for?

Your biggest clue will be how quickly you become sick.

Flu tends to come on more suddenly and intensely than a common cold.

A person with flu may go from feeling well to feeling extremely unwell within a matter of hours, with fever, chills, body aches, headache, cough and fatigue.

Someone who has the cold will experience milder symptoms and is more likely to have a pack of tissues on them due to a runny or blocked nose. There will also be sneezing and a sore throat.

The CDC notes that cold symptoms are usually less intense than flu symptoms and that people with colds are more likely to have a runny or stuffy nose.

This is where it gets a little bit more complicated, as COVID-19 can resemble either one.

The World Health Organization (WHO) says COVID-19 and influenza can both cause symptoms including cough, runny nose, sore throat, fever, headache and fatigue.

Common cold

Common cold symptoms can include runny or blocked nose, sneezing, sore throat, cough, mild headache, mild body aches and tiredness.

Colds are usually less severe than influenza and are less likely to result in serious complications.

Flu

Influenza commonly causes sudden fever or feeling feverish, chills, cough, sore throat, runny or blocked nose, headache, muscle and body aches and tiredness.

The NICD lists sudden onset of fever, muscle pains and body aches, dry cough, sore throat, runny nose and tiredness among the common symptoms of influenza.

It is worth noting that not everyone with flu will have a fever.

COVID-19

COVID-19 may cause fever or chills, cough, sore throat, tiredness, headache, body aches, runny or blocked nose, loss or change of taste or smell, shortness of breath, nausea or vomiting and diarrhoea.

The range of symptoms varies between people, and many cases are mild.

Can you tell flu and COVID-19 apart by symptoms?

No. According to WHO, it is not possible to tell the difference between flu and COVID-19 from symptoms alone. Testing is the only way to establish which virus is responsible, or whether someone has both infections.

The CDC similarly says the symptoms of flu and COVID-19 overlap and that testing is needed to confirm a diagnosis.

That means a high fever and body aches do not automatically mean flu, while a blocked nose and sore throat do not automatically mean a cold.

When should you test for COVID-19?

Consider testing if you develop cold- or flu-like symptoms and think you may have COVID-19, particularly if you are at increased risk of severe illness.

The CDC advises people with cold-like symptoms who suspect COVID-19 or flu to get tested, especially people at higher risk of severe illness.

Testing is also useful when you have recently been exposed to someone with COVID-19 or when you are going to be around someone vulnerable to severe respiratory illness.

There are also tests capable of detecting more than one respiratory virus.

The CDC notes that at-home multiplex tests can detect COVID-19 and flu from a single test.

What if a COVID-19 test is negative?

A negative result does not necessarily mean that your symptoms are caused by a common cold.

This is because, depending on the type of test and when it is taken, an infection may not be detected.

If symptoms continue or worsen, particularly if you are at higher risk of severe illness, speak to a healthcare professional about whether further testing is appropriate.

What about flu testing?

Flu can also be diagnosed through testing, although a healthcare professional may sometimes make a clinical diagnosis based on symptoms, the patient’s risk factors and whether influenza is circulating.

This is particularly important for people at higher risk of complications because antiviral treatment for influenza works best when started early.

The NICD’s 2026 influenza guidance notes that antiviral treatment should be considered for people with severe influenza and those at increased risk of complications, with treatment most effective when started as soon as possible.

When should you see a doctor?

Most people with mild respiratory infections recover without needing hospital treatment, but seek medical attention if symptoms become severe or rapidly worsen.

Urgent medical attention is warranted for symptoms such as difficulty breathing or severe shortness of breath, chest pain or pressure, confusion or difficulty staying awake, severe weakness, signs of serious dehydration, and symptoms that improve and then suddenly become much worse.

People who are at higher risk of severe illness should also contact a healthcare professional early if they develop flu- or COVID-19-like symptoms.

Don’t spread it around

If you are sick, try to avoid close contact with other people, especially older people, young children and people with underlying conditions that put them at greater risk of severe respiratory illness.

Improving ventilation in your home, washing your hands regularly, covering coughs and sneezes and considering a mask in crowded indoor spaces can help reduce the spread of respiratory viruses.

IOL