Serial passage is a virus attenuation technique developed originally by Louis Pasteur in the 1880s. It is similar to selective breeding, and can be used to create an attenuated strain of a virus to develop vaccines, or to increase the virulence of a viral strain in order to create epidemics.. The process involves infecting a series of host organisms with a virus.
Virus growth kinetics and serial passages were performed, and incorporation of the viral segments was tested by real-time RT-PCR. An initial virus growth deficiency correlated to a specific defect in NA segment incorporation. Upon serial passages, growth properties were restored.