Abstract: The present invention provides a novel inactivated virus particle and a reinforced immunogen which have a reinforced titer about twice to about 10 times that of a conventional vaccine, as well as a method for producing the same. The inactivated virus particle is produced by inactivating and then purifying a culture by physical means. The inactivated virus particle of the present invention is useful in a diagnostic agent for infectious disease caused by a group of Japanese encephalitis virus.

Abstract: The present invention provides a method for producing a rotavirus antigen which the mass culture is difficult, comprising cloning a cell highly permitting the proliferation of rotavirus from a cell culture; preparing a cloned cell adapted-rotavirus strain by passaging a rotavirus in the resulting cloned cell strain and adapting the rotavirus to the cloned cell strain; culturing as a seed virus the adapted rotavirus strain or a reassortant prepared by using the adapted rotavirus strain as a parent strain; and isolating and purifying the rotavirus antigen from the culture medium of the seed virus; and additionally provides an rotavirus antigen, a vaccine against rotavirus infections, and a diagnostic agent of the diseases, as produced by using the antigen. These antigen, vaccine and diagnostic agent can make great contributions to individual fields of the fundamental research works and clinical application, relating to rotavirus infections.