Heterogeneity of A/Singapore/1/57 (H2N2) influenza virus

The population of A/Singapore/1/57 (H2N2) influenza virus was found to contain two types of infectious particle. "Normal" virions with a diameter from 100-130 nm, a buoyant density in sucrose of 1.21 g/cm3 and a sedimentation coefficient 770 S represented about 90 percent of the population. In addition, a considerable amount of larger particles (up to 1000 nm) with a buoyant density in sucrose of 1.18 g/cm3 and a sedimentation coefficient of over 1000 S were present.