Antigenic analysis of a putative new strain of respiratory syncytial virus.

A recent isolate (9320) of respiratory syncytial virus (RSV) that had been reported to differ from all previous strains was compared with RSV strains isolated over a period of 23 years by using the techniques of in vitro neutralization by specific antiserum and in vivo resistance to infection in cotton rats. The 9320 strain did not appear to be a novel antigenic variant and exhibited greater homology to several prototype strains than did an earlier isolate. The antigenic differences detected by in vitro neutralization disappear when virus strains are compared in vivo. Thus, it appears that concerns that antigenic instability might compromise efforts at RSV prophylaxis are unfounded.