Influenza (Seasonal)

Influenza virus types A and B are both common causes of acute respiratory illnesses.

Severe morbidity and mortality more common among elderly people and in specific high-risk groups.

Influenza viruses undergo frequent changes in their surface antigens, with new influenza outbreaks occurring every year.

Influenza viruses spread from person to person, primarily through respiratory droplets.

General symptoms are generally localised to the respiratory tract and include nonproductive cough, fever, headache, malaise, muscle aches, rhinitis and sore throat.

Illness without fever can occur, especially in older adults and infants.

Complications of influenza virus infection include primary influenza viral pneumonia and secondary bacterial pneumonia, as well as ear and sinus infections and worsening of chronic medical conditions (congestive heart failure, asthma, diabetes).