Ingredients in flu vaccinations vary because there are 16 different influenza vaccines that are used in the United States, explains the National Vaccine Information Center. Flu vaccinations are prepared with fluids from chick embryos and varying types of flu viruses, inactivated with formaldehyde and preserved with a preservative such as thimerosal.
Some vaccines contain thimerosal and one type of flu strain, while others contain no thimerosal and three types of flu strains, according to the National Vaccine Information Center. Inactivated injectable vaccine that is packaged in multi-dose vials contains the mercury preservative thimerosal, while inactivated influenza vaccine that is packaged in single-dose vials contains no trace elements of thimerosal. Another example of varying ingredients is the influenza vaccination FluMist, which contains MSG and an antibiotic called Gentamicin, as well as other ingredients.
As different pharmaceutical companies manufacture and distribute the various types of vaccine, the ingredients may vary, according to the National Vaccine Information Center. Influenza vaccines are considered category B or C drugs. This means that adequate scientific studies have not been conducted in regard to pregnancy or reproduction. As of 2015, it is not known if influenza vaccine harms a fetus or affects the ability to reproduce. A complete listing of influenza vaccine inserts and packaging can be found at nvic.org.