The ingredients typically found in flu vaccines include antigens, stabilizers, adjuvants and preservatives, according to the Centers for Disease Control and Prevention. Additional ingredients include residual antibiotics, residual cell culture materials and residual inactivating ingredients such as formaldehyde.
The antigens in flu vaccines cause the body to create antibodies used to combat flu viruses, states MedlinePlus. Stabilizers, such as gelatin or sugars, help keep flu vaccines intact during transport to hospitals and clinics, explains the CDC. Adjuvants, such as aluminum salts, assist the body so it can adequately respond to the antigens.
Preservatives such as thimerosal, which is also known as mercury, help prevent contamination from multiple flu vaccination needles that are injected into a single vial, explains the CDC. Thimerosal, found only in multi-dose flu vaccines, can cause redness around the injection site. It is not present in single-dose vaccines.
The residual antibiotics, such as neomycin, help prevent bacteria from contaminating newly made vaccines, the CDC reports. Residual cell culture materials, such as egg protein, help vaccine manufacturers grow the correct amount of a specific virus to create an effective vaccine. A small amount of formaldehyde can kill a virus and prevent overspreading of a virus during production. Formaldehyde also kills any inactive toxins that are not necessary to create an effective flu vaccine.