What other ingredients do vaccines contain?

In addition to viruses, bacteria or toxoids, vaccines often contain other ingredients that are included in the vaccine for a specific reason. These other ingredients are usually present in tiny amounts and are generally not harmful in such small quantities.

People may need to know about these other vaccine ingredients in case of any allergy, food intolerance, or religious or cultural dietary limitations.

Vaccines rarely cause allergies or anaphylaxis (a serious form of allergic reaction that happens rapidly). If you do have any allergies, or you have had a bad reaction to any vaccine or medicine in the past, tell your doctor.

Other ingredients contained in vaccines include:

  • preservatives to make sure the vaccine does not become contaminated with fungi or bacteria (preservatives are not present in all vaccines)
  • additives to help keep all the ingredients in the vaccine stable when it is stored and to prevent the vaccine from sticking to the walls of the vial so that it stays active and effective
  • adjuvants to improve your body’s immune response to the vaccine so that smaller amounts of the virus or bacteria are used in the vaccine
  • liquid to dilute the vaccine to the right dose
  • tiny amounts of other ingredients left over from the process used to produce the vaccine; for example, the flu vaccine may contain egg proteins as the viruses used in the vaccine are grown in a live hen’s egg.

For more in-depth information read the vaccine ingredients factsheet and see our FAQs.