Making a vaccine can be hard. The development work might take years. Part of the challenge is the way that flu vaccines are manufactured, using chicken eggs to culture the virus and grow the critical proteins that are used as the stock for the vaccines. Under this process, a fertilized chicken egg is inoculated with a strain of influenza. The virus is allowed to replicate in the yolk, before it’s harvested, inactivated, and incorporated into vaccines. In this way, the eggs serve as incubators for the development of the viral proteins that are used for the vaccine.
