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. Medical uses The live attenuated influenza vaccine is used to provide protection against the flu caused by infection with influenza viruses. Contraindications The use of the live attenuated influenza vaccine is contraindicated, and should therefore not be used, in the following populations: children <24 months of age, due to increased risk of wheezing individuals with a history of hypersensitivity to previous influenza vaccination. individuals with a history of hypersensitivity, especially anaphylactic reactions, to eggs, egg proteins, gentamicin, gelatin, or arginine or to any other ingredient in the formulation People with a medical condition that places them at high risk for complications from influenza, including those with chronic heart or lung disease, such as asthma or reactive airways disease People with medical conditions such as diabetes or kidney failure or people with illnesses that weaken the immune system, or who take medications that can weaken the immune system Children less than 5 years old with a history of recurrent wheezing Children or adolescents receiving aspirin People with a history of Guillain–Barré syndrome, a rare disorder of the nervous system Pregnant women People who have a severe allergy to chicken eggs or who are allergic to any of the nasal spray vaccine components Production The live attenuated vaccine is based on a flu strain that does not cause disease, that replicates well at relatively cold temperatures (about 25 °C, for incubation purposes), and replicates poorly at body temperature (which minimizes risk to humans). Genes that code for surface proteins (targeted antigens) are combined with this host using genetic reassortment from strains that are projected to be circulating widely in the coming months. The resulting viruses are then incubated in chicken eggs and chick kidney cells. To make the refrigerated version, the virus is purified in centrifuges through a sucrose gradient, then packaged with sucrose, phosphate, glutamate, arginine, and gelatin made from pigs that has been hydrolyzed with acid. Risks Even