[Molecular basis of the variability of epidemic strains of human influenza viruses].

The data from literature and authors own studies are reviewed on variability of human influenza viral strains, isolated during the same epidemic season in different periods of pandemic cycle. The data obtained indicate that variability of epidemic strains of human influenza virus deals with the genes coding for outer membrane proteins (hemagglutinin and neuraminidase) as well as nonglycosylated proteins. Circulation of a number of viral variants of the same serotype, differing in antigenic specificity of outer membrane proteins or in the genes coding for nonglycosylated proteins was registered during one and the same season of one epidemic. During circulation of viral variants of the same serotype recombination may take place. Heterogeneity of viral strains circulating during different epidemic seasons of the same pandemic cycle is different. The possible mechanisms of development of the new epidemic variants of human influenza virus are discussed.