The invention relates to a method for producing the flu virus, that comprises: a) administering a flu vaccine to hens; b) collecting the eggs of the vaccinated hens; c) triggering the embryogenesis process; d) infecting the embryonated eggs by inoculating a flu virus in the allantoic cavity; e) incubating the infected embryonated eggs in temperature and humidity conditions allowing the virus replication; and f) collecting the allantoic liquid containing the virus.
