The present invention relates to a 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. The present invention employs solvents useful for extracting lipids from the lipid-containing infectious viral organism thereby creating modified viral particles with reduced infectivity and enhanced antigenicity. The present invention provides vaccine compositions, comprising these modified viral particles with reduced infectivity and enhanced antigenicity, optionally combined with a pharmaceutically acceptable carrier or an immunostimulant. The vaccine composition is administered to a patient to provide protection against 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.