The CDC states:

“-Seasonal influenza (flu) vaccines are designed to protect against the three influenza viruses that are expected to circulate most widely during the upcoming season.

-CDC is working with other federal agencies and the private sector, to improve flu vaccine technologies.

-Three different flu vaccine production technologies are FDA approved for use in the United States: egg-based flu vaccine, cell-culture based flu vaccine, and recombinant flu vaccine.

Influenza (flu) vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the influenza viruses that are used to make vaccine. The seasonal flu vaccine protects against the influenza viruses that research suggests will be most common during the upcoming season. These include three different main groups of influenza Type A and B viruses.”

Center for Disease Control and Prevention – CDC (How Influenza (Flu) Vaccines Are Made | Influenza (Flu) | CDC&Different Types of Flu Vaccines | Influenza (Flu) | CDC)