Influenza - Seasonal

What is influenza?

Seasonal influenza, commonly known as the flu, is an acute respiratory infection caused by influenza viruses. The disease can cause mild to severe illness, sometimes leading to death. There are three main types of influenza viruses – Type A, B and C. Influenza A (H1N1-2009), Influenza A (H3N2), and Influenza B are the predominant strains circulating globally and in Singapore. Influenza C is associated with mild sporadic illness and occurs less frequently.

Influenza A and B viruses circulate year-round in Singapore, with bimodal peaks typically observed in May to August and December to March. These peaks correspond approximately with influenza seasons in temperate regions of the Southern (generally from April to September) and Northern hemispheres (generally from October to March).

How is influenza transmitted?

Influenza spreads mainly through the respiratory droplets or tiny particles released when an infected person coughs, sneezes, talks or sings. Other people can breathe in these droplets and particles, or these droplets and particles can land on others’ eyes, nose, or mouth.

The virus can also be spread indirectly when a person touches a contaminated surface (e.g. doorknob, utensils) then touches his or her eyes, nose or mouth.

The incubation period is typically 2 days, ranging from 1 to 4 days.

What are the symptoms of influenza? 

The signs and symptoms of seasonal influenza range from mild respiratory symptoms to severe illnesses such as pneumonia.

Common symptoms include:

• Fever

• Chills

• Headache

• Cough

• Sore throat

• Muscle aches

• General malaise and fatigue

• Gastrointestinal symptoms, such as nausea, vomiting, or diarrhoea, more commonly in children

In severe cases, influenza can result in pneumonia, hospitalisation or even death, especially in populations at higher risk of developing severe disease.

What are the risk factors?

Individuals at greater risk of severe disease or complications when infected include:

• Persons aged 65 years and above

• Children aged 6 months to under 5 years

• Adults and children with chronic pulmonary or cardiovascular disorders

• Adults and children who have been hospitalised or require ongoing medical care due to chronic conditions affecting metabolism, kidneys, nervous system, liver, or blood disorders

• Adults and children with immunosuppression

• Children and adolescents aged 6 months to 18 years who are receiving long-term aspirin therapy and therefore might be at risk for developing Reye syndrome after influenza infection

• Pregnant women

How is influenza treated?

Seasonal influenza is usually mild and self-limiting. Supportive care and symptom-relieving treatment, such as treatment with fever-reducing medications, staying well-hydrated, and getting enough rest, are usually enough to manage the acute symptoms of influenza.

Antiviral medications can be prescribed by doctors for the treatment of influenza infection. They can help reduce the severity and duration of symptoms, as well as promote recovery. They are most effective within the first 2 days of illness.

How to prevent influenza?

Individuals at a higher risk of developing severe influenza infections, such as seniors and other vulnerable persons with underlying medical conditions, are recommended to consult their attending physician and receive their influenza vaccinations as per the prevailing national vaccination recommendations. For more information on the national influenza vaccine recommendations, please refer to this page.

Other preventive measures include:

• Observing and practising good personal hygiene at all times

• Washing your hands regularly with soap, especially before handling food or eating, after going to the toilet, or when hands are dirty from coughing or sneezing. If water is not available, use an alcohol-based hand sanitiser that contains at least 60% alcohol

• Covering your mouth with a tissue when coughing or sneezing and dispose the soiled tissue into the bin immediately. Avoid touching your face, including eyes, nose and mouth with unwashed hands after coughing or sneezing

• Avoiding sharing of food/drinks or eating utensils

• Wearing a mask and seeking medical attention promptly when unwell

Please refer to Health Advice for Travellers for the full list of precautions to take when travelling.