[14][15][3] The use of the live attenuated influenza vaccine is contraindicated, and should therefore not be used, in the following populations: 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.

MedImmune, Inc. purchased Aviron in 2002, and the US Food and Drug Administration (FDA) approved the live attenuated influenza vaccine in June 2003.

[20][11] The FDA initially approved the live attenuated influenza vaccine only for healthy people aged 5 to 49 because of concerns over possible side effects.

The live attenuated influenza vaccine is approved and recommended for healthy children 24 months of age and older.

Approved for the 2007-2008 flu season,[11] the refrigerated formulation can be distributed more economically, so that the price differential with shots (which had hampered sales of the original frozen version of FluMist) is now largely eliminated.

[6] As of 2007[update], the only other company holding live attenuated influenza vaccine rights is BioDiem of Australia.

[12] The live attenuated influenza vaccine is designed to be quickly modifiable to present the surface antigens of seasonal flu.

[39] In September 2006, the National Institute of Allergy and Infectious Diseases (NIAID) reported that inoculation with a live attenuated influenza vaccine modified to present the surface antigens of certain H5N1 variants provided broad protection against other H5N1 variants in the mouse and ferret models.

(58, 59)[42] "[V]accine formulas inducing heterosubtypic T cell–mediated immunity may confer broad protection against avian and human influenza A viruses.