Influenza, seasonal influenza, or "the flu" is an infection of the airways—the nose, throat, and lungs—caused by the influenza viruses. Anyone can be affected, but certain populations are more vulnerable to developing severe disease, such as children, pregnant women, the elderly, and persons with chronic or immunocompromising conditions such as asthma, diabetes, heart disease, or obesity.

Last Updated: September 26, 2023

There are three main types of influenza virus (types A, B, and C) that affect humans, each of which has many different strains and causes varying severity of infections. The influenza virus is mainly transmitted through droplets: A person can become infected by inhaling very tiny droplets containing the virus when an infected person coughs, sneezes, talks, or eats. These droplets can land in the nose or mouth, or on objects that are then touched by a person who subsequently touches their eyes, nose, or mouth with that infected hand. People can already be infectious one day before their symptoms appear.

• Fever, or feeling feverish
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle and joint pain
• Severe malaise (feeling unwell)
• Headache
• Chills
• Vomiting and diarrhea in some cases

Most people will recover from with only supportive management (e.g., bed rest, increased fluid intake, good nutritional diet). Patients admitted to hospitals may be given anti-viral medications like oseltamivir, so it is very important for people displaying flu-like symptoms to consult a doctor immediately or inform proper health authorities. Antivirals are most effective if given within the first 48 hours after symptoms appear. 

For children under 16 years old with fever and muscle aches, aspirin should not be given, as this may lead to a reaction called Reye's Syndrome; instead, paracetamol is advised

• Get vaccinated annually for influenza. Because the viruses mutate easily, the annual vaccines are also modified, so it is important to get them every year.
• Wash hands frequently with soap and water.
• Cover the mouth and nose when sneezing or coughing to prevent the spread of the virus.
• Self-isolate early when feeling unwell, feverish, or experiencing other symptoms of influenza.
• Avoid close contact with sick people.
• Avoid touching your eyes, nose, or mouth.

Last Updated: September 26, 2023