Live attenuated influenza vaccine (LAIV) is a type of influenza vaccine in the form of a nasal spray that is recommended for the prevention of influenza. It is an attenuated vaccine, unlike most influenza vaccines, which are inactivated vaccines. LAIV is administered intranasally, while inactivated vaccines are administered by intramuscular injection. LAIV is sold under the brand name FluMist Quadrivalent in the United States and the brand name Fluenz Tetra in the European Union. FluMist was first introduced in 2003 by MedImmune.