Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world.
- Seasonal influenza is an acute viral infection that spreads easily from person to person
- Seasonal influenza viruses circulate worldwide and can affect people in any age group
- In temperate climates, seasonal epidemics occur mainly during winter while in tropical regions, influenza seasonality is less obvious and epidemics can occur throughout the year
- Seasonal influenza is a serious public health problem that causes severe illness and death in high risk populations
- An influenza epidemic can take an economic toll through lost workforce productivity and strained health services
- Influenza vaccination is the most effective way to prevent disease
- Antiviral drugs are available for treatment
Signs and Symptoms
Seasonal influenza 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 can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death especially in people at high risk (see below).
Illnesses range from mild to severe and even death. Hospitalization and death occur mainly among high risk groups. Worldwide, these annual epidemics are estimated to result in about 3 to 5 million cases of severe illness, and about 290 000 to 650 000 deaths.
In industrialized countries most deaths associated with influenza occur among people age 65 or older. Epidemics can result in high levels of worker/school absenteeism and productivity losses. Clinics and hospitals can be overwhelmed during peak illness periods.
The effects of seasonal influenza epidemics in developing countries are not fully known, but research estimates that 99% of deaths in children under 5 years of age with influenza related lower respiratory tract infections are found in developing countries.