 According to the personal memory of Alisa G. Bukrinskaya, who has co-authored numerous publications related to SeV along with Prof. Viktor M. Zhdanov, starting in 1961, the Moscow strain of SeV was obtained by Prof. Viktor M. Zhdanov of the Ivanovsky Institute of Virology from Japan in the late 1950s or early 1960s, It is reported that the BB1 strain derived from the Moscow virus strain.The strain BB1 was given to the researchers of Institute of Viral Disease Control and Prevention, Beijing, China by researchers of Ivanovsky Institute of Virology, Moscow, Russia in 1960s.A field SeV isolate, that is attenuated through egg-passages, is less virulent for mouse respiratory cells.