Seasonal influenza is an acute respiratory infection caused by influenza viruses, which circulate in all parts of the world and can affect people in any age group. The virus particles are transmitted easily from person to person via respiratory droplets and small particles produced when infected people cough or sneeze.

Seasonal influenza causes illnesses that range in severity and sometimes lead to hospitalization and death. Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death, particularly among high risk groups including the very young, the elderly, pregnant women, health workers, and those with serious medical conditions. It is characterized by a sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose. The cough can be severe and last two or more weeks. The time from infection to illness is about two days.

In temperate climates, seasonal epidemics occur mainly during winter, while in tropical regions, influenza may occur throughout the year, causing outbreaks more irregularly. Influenza tends to spread rapidly in seasonal epidemics. Influenza epidemics can take an economic toll through lost workforce productivity and strained health services.

For patients that are not in a high risk group, treatment focuses on relieving symptoms of influenza such as fever. Patients that are known to be in a group at high risk for developing severe or complicated illness should seek medical attention and should be treated with antiviral drug as soon as possible. Ideally, antivirals need to be administered within 48 hours of the onset of symptoms although influenza viruses can develop resistance to the drugs. The use of antivirals may reduce severe complications and deaths.

To prevent transmission, people should cover their mouth and nose when coughing or sneezing and wash their hands regularly. Beyond this the most effective way to prevent influenza is through vaccination. Safe and effective vaccines are available and have been used globally for more than 60 years.

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Related links

Global influenza strategy 2019-2030

Flu vaccination toolbox

Pandemic Influenza Preparedness (PIP) Framework

Epidemic- and pandemic-prone diseases