evidence: The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses. Influenza, caused by influenza virus strains of special epidemiological importance with an animal-human or inter-human transmission. [...] Diseases in the Influenza family