Antigenic and biological criteria of differentiation of the newly isolated strains of respiratory syncytial virus.

Respiratory syncytial (RS) virus strains isolated in different years varied by their antigenic and biological properties. The lowest degree of relatedness was found between the "street" virus and the prototype Long strain; the highest occured among the isolates from a given isolation period. Based on the mean indices of efficiency of the virus reproduction in human embryo lung (HEL) cells at 37 degrees C and 39 degrees C as well as on the degree of virus sensitivity to reference antibodies, the isolates from various years could be divided into three groups, namely high, mild and low virulent strains. The incidence of RS virus infections in children depended on the strain characteristic of virus population circulating in a community of children during the long-term observation period of 1976-1979. Cyclic variation was found in isolation rates of RS viruses; the duration of each cycle in different years ranged from 21 to 41 days. The variability of isolation cycles and the frequency of RS virus reinfections were closely related to the biological characteristics of circulating virus strains.