Mission: To save lives and reduce hospitalizations by protecting children, families, and communities against influenza.

Vaccine Ingredient Safety

Vaccine ingredients are tested for safety before they are manufactured. Learn more about each ingredient:


  • Sodium & aluminum salts are used to normalize the salt balance in the human body
  • Some salts split the virus into smaller pieces to activate the immune system for adjuvanted vaccines


  • Adding sugar stabilizes the vaccine ingredients so that they are less sensitive to heat/cold
  • The sugars used in vaccines are the same ones used to stabilize food products


  • Help mix ingredients that would normally not mix together (think oil + vinegar!)
  • The amounts used in vaccines are much smaller than what is used in other things you put into your body - like food and cosmetics

MF59 Adjuvant

  • Only used in adjuvanted vaccines for people 65+ to create a stronger immune response
  • The main ingredient, squalene oil, occurs naturally in humans, animals, and plants


  • Preservative used to prevent contamination in multi-dose vials
  • Most flu vaccines are single-vial and thus do not contain thimerosal
  • Thimerosal is metabolized by the body as ethylmercury, which is not the same as methylmercury, and does not cause poisoning


  • Formaldehyde is naturally occurring in apples, bananas, pears, and more
  • Used to kill the flu viruses so that the viruses in the vaccine teach your body to fight off and don't make you sick
  • The amount used in vaccines is much smaller than the amount that naturally occurs in the body


  • Can be leftover from the manufacturing process to prevent contamination of bacteria into the vaccines
  • Most are removed during the purification process
  • The amount leftover is microscopic


  • Only present in vaccines grown in eggs
  • Most is filtered out when the viruses are extracted from the eggs they were grown in

Learn more about flu and flu vaccines:

Page last reviewed: November 2021.

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