What is influenza?

Influenza, also known as “flu” is an acute respiratory illness caused by an infection of the respiratory tract with the influenza virus. There are two types of influenza viruses that commonly infect humans namely A and B. The flu viruses are typically in circulation before the winter months in South Africa with an average start of the flu season in the first week of June, although this varies.

Are there different types of influenza?

The influenza virus has two main types in humans: A and B. Influenza A is classified into different subtypes influenza A(H1N1)pdm09 and A(H3N2). Influenza A(H1N1)pdm09, which has colloquially been called “swine flu”, is the human influenza strain that emerged globally in 2009. This strain behaves like any other strain of seasonal influenza and infected patients should be treated like any other seasonal influenza case. There are no specific public health interventions required for patients or contacts of patients infected with influenza A (H1N1)pdm09. The term “swine flu” should not be used, because this term refers to influenza in pigs.

How is influenza transmitted?

The virus is spread from person to person. It can be passed from infected people to other people through inhalation of infected respiratory droplets from sneezing, coughing or talking. A person can also be infected by touching contaminated objects or surfaces that the flu virus is on and then touching their mouth, eyes or nose. People who are infected with influenza can prevent spread by doing the following:

  • Covering their mouth when coughing with a tissue or cough into the elbow
  • Wearing a cloth mask
  • Washing their hands frequently with soap and water or cleaning hands using an alcohol-based sanitiser
  • Staying at home and trying to keep a distance from others 

What are the signs and symptoms of influenza in humans?

The most common symptoms in infected patients are sudden onset of fever, muscle pains and body aches, dry cough, sore throat, runny nose, feeling tired or unwell and headache. The symptoms develop anywhere from 1 to 4 days after infection and last for 2 to 7 days. For the majority of people, the symptoms commonly resolve without treatment. Complicated influenza infections can cause serious illness and in some cases death. Severely ill patients with influenza should be admitted to the hospital. The commonest complication of influenza is pneumonia.

Who is at most risk for influenza?

Influenza infection resulting in mild illness is most common in children of school-going age between 5 and 15 years. Influenza can also cause severe illness and the following groups of people are at the highest risk of severe illness: children aged <5 years, adults aged 65 years or older, pregnant women, those who are obese (BMI ≥40) and those with chronic health conditions such as chronic heart disease, chronic lung disease (e.g. TB), kidney, liver, blood or metabolic diseases (e.g. diabetes), or weakened immune systems (e.g. HIV infection).

How is influenza diagnosed?

Influenza is normally a clinical diagnosis and not all patients require testing for diagnosis. Testing for diagnosis can be done to assist in the treatment and when there are a higher number of cases than expected to identify outbreaks. When testing is needed respiratory samples can be collected and these include nasopharyngeal or nasal swab, nasal wash or aspirate, throat swab and sputum.

How is influenza treated?

The majority of infected people will only need bed rest, adequate fluid intake and paracetamol to help with the fever or aches. The more severe cases may need antiviral drugs for influenza that can only be prescribed by a medical doctor. The drugs are ideally administered early (within 48 hours of the onset of symptoms) in the disease. Antiviral treatment may also be used for people at risk of severe influenza early in the infection. People at risk for severe influenza illness or complications should consult their doctor early in the illness.

How can influenza be prevented?

Influenza vaccination is the best way to prevent influenza infection. The influenza virus is constantly changing and vaccination for influenza has to be re-done every year. The vaccine is an inactivated virus that is not harmful and cannot cause flu infection. It only offers protection 2-3 weeks after administration. So ideally the flu vaccine should be done early (March/April each year) before the Flu season so that it has sufficient time to protect a person. However, it is never too late to vaccinate.

In 2021 with the circulation of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) the virus that causes Coronavirus Disease 2019 (COVID-19) we recommend the influenza vaccine as it is likely that the 2 viruses will be circulating at the same time and the flu vaccine may help to decrease the burden on our healthcare system.

Groups recommended to receive influenza vaccination in 2021 include:

  • Healthcare workers
  • Persons aged ≥ 65 years
  • Persons with underlying chronic health conditions
  • HIV–infected adults
  • Pregnant women at any stage of pregnancy, or postpartum
  • Residents of old-age homes, chronic care and rehabilitation institutions
  • Persons aged 6 months to ≤18 years on long-term aspirin therapy
  • Children aged 6 months to 5 years and their household contacts or caregivers
  • Any persons wishing to minimise the risk of influenza acquisition.

What is the difference between the flu and COVID-19?

While influenza and COVID-19 are both contagious respiratory illnesses caused by viruses, the viruses that cause them are not the same. COVID-19 is caused by infection with a new coronavirus (called SARS-CoV-2), and flu is caused by infection with influenza viruses. Both viruses can cause mild to severe illness and present with similar symptoms including fever, cough, sore throat, shortness of breath, runny or blocked nose, muscle pains/body aches and fatigue. COVID-19, on the other hand, seems to spread more easily than flu and can result in a more serious illness in certain people. Other signs and symptoms of COVID-19, different from flu, may include a change in or loss of taste or smell. COVID-19 infected people can also take longer to show symptoms, and they can be contagious for longer periods. Since some flu and COVID-19 symptoms are similar, it may be difficult to differentiate between them based on symptoms alone, and laboratory testing may be needed to confirm a diagnosis.

Can I get flu and COVID-19 at the same time?

Yes, it is possible to have both the flu and COVID-19 at the same time if both viruses are circulating in the community. If you suspect that you have either of the diseases, it is recommended that you go to your doctor or clinic for further assessment.

Do I have to take the influenza vaccine if I have the SARS-CoV-2 vaccine or vice versa?

Yes. The influenza vaccine will protect you against influenza and the SARS-CoV-2 vaccine will protect you against COVID-19. A minimum of 14-days waiting period between the 2 vaccines is recommended.

Where can I find out more information

Guidelines and other useful resources are available on the NICD website.

Additional information on influenza is available on the following website references:

For the public:

U.S. Centers for Disease Control and Prevention (CDC):

World Health Organization Fact sheet on Influenza disease:

For healthcare workers:

  • Contact the NICD hotline (+27 82 883 9920) after hours and in emergency situations
  • NICD recommendations for the diagnosis, management, prevention and public health response are available here.

Diseases A-Z Index



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