The flu (influenza) is a highly contagious infection that affects the lungs. Learn about its signs and symptoms and how getting vaccinated prevents it from spreading. Translations are given in Amharic, Arabic, Burmese, Chinese (Simplified), Dari, Dinka, French, Japanese, Karen, Khmer (Cambodian), Samoan, Spanish, Swahili, Tagalog (Filipino), Thai and Vietnamese.