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 live vaccine, unlike other influenza vaccines, which are inactivated vaccines. LAIV is administered intranasally, while inactivated vaccines are administered by intramuscular injection. LAIV is sold under the brand names FluMist and FluMist Quadrivalent in the United States; and the brand name Fluenz Tetra in the European Union. FluMist was first introduced in 2003 by MedImmune. In the United States, FluMist is approved for self- or caregiver-administration. It is the first influenza vaccine that does not need to be administered by a health care provider.
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 it should therefore not be used, in the following populations:
Children under 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 (77 °F), 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 hydrolyzed pig gelatin.
Risks Even though the virus in the live attenuated influenza vaccine (LAIV) is attenuated (low in virulence), it is still a living virus, and may cause an infection with complications in people with weakened immune systems or other underlying medical conditions. LAIV is recommended only for people 2–49 years of age, and people who have a weakened immune system, pregnant women, and people with certain chronic diseases may not be eligible to receive the vaccine. In contrast, inactivated virus vaccines contain no living virus, and cannot cause a live infection. Persons receiving LAIV may shed small amounts of the vaccine virus during the first week. People coming in contact with the vaccinated person are not considered to be at risk, unless their immune systems are severely weakened (for example, bone marrow transplant recipients).
History The live attenuated influenza vaccine (LAIV) was developed by the University of Michigan School of Public Health in Ann Arbor, Michigan and later by Aviron, in Mountain View, California, under the sponsorship of the National Institutes of Health (NIH) in the 1990s. MedImmune purchased Aviron in 2002, and the US Food and Drug Administration (FDA) approved LAIV in June 2003. The FDA initially approved LAIV only for healthy people aged 5 to 49 because of concerns over possible side effects. LAIV is approved and recommended for healthy children 24 months of age and older. The FDA approved the unfrozen refrigerated version for the same age group (ages 5–49) in August 2006, following completion of phase III clinical trials. The cold-adapted version of the vaccine is called CAIV-T, and is stable for storage in a refrigerator, rather than requiring freezer storage as did the originally-approved formulation. Approved for the 2007-2008 flu season, the refrigerated formulation can be distributed more cheaply, making it more price-competitive with injected vaccines. The higher price hampered sales of the original frozen version of FluMist; FluMist was initially priced higher than injectable vaccines, and sold only 500,000 of the four million doses produced its first year on the market, despite a comparative shortage of flu vaccine in fall 2004. The price was sharply lowered the next year, and MedImmune reported distributing 1.6 million doses in 2005. Because of the price drop, despite selling almost three times as many doses in 2005, the company reported $21 million in revenue from FluMist sales, compared to $48 million the previous year.
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