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-adaption.
