APA Dictionary of Psychology

n. a highly contagious respiratory illness caused by influenza viruses, typically types A and B, that spreads primarily through respiratory droplets and aerosols. It often begins abruptly, with symptoms such as fever, chills, cough, sore throat, nasal congestion, muscle or body aches, headache, and profound fatigue; some individuals, especially children, may also experience gastrointestinal symptoms. Illness severity ranges from mild to life threatening and can lead to complications such as pneumonia, worsening of chronic conditions, hospitalization, or death. People at elevated risk include older adults, young children, pregnant individuals, and those with certain chronic medical conditions or weakened immune systems. Most otherwise healthy people recover with supportive care, though antiviral medications can reduce severity when started early. Annual vaccination remains an effective strategy for reducing the risk of infection and serious outcomes. Also called flu.