Questions & Answers About the Influenza Vaccine 

When did influenza vaccine first become available?
The first influenza vaccine in the U.S. became available in 1945. 

What kind of vaccine is it?
There are two types of influenza vaccine. The most common influenza vaccine is made from inactivated (killed) viruses. In June 2003, a live influenza vaccine was licensed. It contains live viruses that have been weakened (attenuated). 

How are the vaccines made?
Every year, researchers and manufacturers develop a vaccine that contains virus strains they believe will be circulating in the upcoming influenza season. Influenza vaccine contains three viruses—two type A and one type B. The viruses selected for the vaccine are grown in chicken eggs. For inactivated vaccine, the viruses are killed with formaldehyde, purified, and packaged in vials or syringes. The live vaccine is packaged in a special sprayer. About six months are required to produce influenza vaccine each year. 

How is the vaccine given?
The inactivated vaccine is given as an injection in the deltoid muscle. The live attenuated vaccine is sprayed into the nose