Described are a composition and method for reducing the occurrence and severity of infectious diseases, especially infectious diseases in which lipid-containing infectious viral organisms are found in biological fluids, such as blood. Solvents useful for extracting lipids from lipid-containing infectious viral organisms are employed thereby creating immunogenic modified, partially delipidated viral particles with reduced infectivity. Provided are delipidated viral vaccine compositions, such as therapeutic vaccine compositions, comprising these modified, partially delipidated viral particles with reduced infectivity, optionally combined with a pharmaceutically acceptable carrier or an immunostimulant. The vaccine composition is administered to a patient to provide protection against a lipid-containing infectious viral organism or, as a therapeutic vaccine, to treat or alleviate infection by the lipid-containing infectious viral organism. The vaccine compositions of the present invention include combination vaccines of modified viral particles obtained from one or more strains of a virus and/or one or more types of virus.