The present invention provides experimentally-generated cold-adapted
equine influenza viruses, and reassortant influenza A viruses comprising
at least one genome segment of such an equine influenza virus, wherein
the equine influenza virus genome segment confers at least one
identifying phenotype of the cold-adapted equine influenza virus, such as
cold-adaptation, temperature sensitivity, dominant interference, or
attenuation. Such viruses are formulated into therapeutic compositions to
protect animals from diseases caused by influenza A viruses, and in
particular, to protect horses from disease caused by equine influenza
virus. The present invention also includes methods to protect animals
from diseases caused by influenza A virus utilizing the claimed
therapeutic compositions. Such methods include using a therapeutic
composition as a vaccine to generate a protective immune response in an
animal prior to exposure to a virulent virus, and using a therapeutic
composition as a treatment for an animal that has been recently infected
with a virulent virus, or is likely to be subsequently exposed to
virulent virus in a few days whereby the therapeutic composition
interferes with the growth of the virulent virus, even in the absence of
immunity. The present invention also provides methods to produce
cold-adapted equine influenza viruses, and reassortant influenza A
viruses having at least one genome segment of an equine influenza virus
generated by cold-adaptation.