Understanding respiratory illnesses: Flu, COVID-19, or just a cold?

As September approaches, South Africans continue to experience the chill of winter, with the respiratory virus season still in full swing and influenza remaining prevalent.

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.

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 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.