Influenza vaccine
Influenza virus causes severe inflammation of all respiratory tissue. Illness includes an abrupt onset of fever, cough, and chills, and severe pneumonia may ensue. Infection occurs via airborne droplets from ill people and occurs in cool months in temperate climates and year-round in the tropics. Adults should receive 1 dose of influenza vaccine each year, because the vaccine lasts only for the current influenza season. Vaccine is given by injection (killed virus vaccines) or nasally (live virus vaccine). Various formulations exist for different patient populations or risk groups. Serious side effects are rare.