Influenza

an acute infectious respiratory disease, caused by influenza viruses, which attacks the respiratory epithelial cells and produces a catarrhal inflammation; characterized by sudden onset, chills, fever of short duration, severe prostration, headache, muscle aches, and a cough that usually is dry until secondary infection occurs

Description
Influenza commonly occurs in epidemics, sometimes in pandemics. Strain-specific immunity develops, but mutations in the virus are frequent, and the immunity usually does not protect against antigenically different strains. This is the reason why high-risk persons who need prophylaxis have to be vaccinated with a new vaccine each year. Syn flu, grippe, grip