What host is used to make the flu vaccine?

The flu vaccine is typically made using chicken eggs, which serve as a host for the influenza virus. The virus is injected into fertilized chicken eggs, where it replicates. After a period of incubation, the virus is harvested, inactivated (or attenuated, in the case of live attenuated vaccines), and then processed to create the vaccine. Some newer vaccine production methods also use cell cultures or recombinant technology to produce the vaccine.