Studies of natural population variability of parainfluenza viruses during their epidemic circulation.

: The population of circulating serotype 3 parainfluenza virus strains isolated in different years proved to be sufficiently polymorphic concerning its antigenic and biological features as well as their virulence for newborn hamsters. The highly virulent strain population appeared to have an antigenic pattern different from that of the prototype strain. The epidemic caused by it in groups of school and preschool children was more intensive as compared to that induced by avirulent strains population.