Vaccine Ingredients

Vaccine ingredients can be confusing to understand. Don’t fear! Let’s look at each kind of ingredient, one at a time.

All vaccine ingredients play a role.

Vaccines are carefully made to include the exact ingredients they need to be safe and effective at preventing disease. All vaccine ingredients play a role. They work to make the vaccine effective, keep it safe from contamination, and build immunity. They have nothing extra or dangerous. Before approving any vaccine, the Food and Drug Administration (FDA) requires the vaccine to undergo lots of testing to ensure all the ingredients it contains are safe. Parents and caregivers can be assured that components of their child’s vaccines are not harmful. They work to keep children healthy and protected against infectious diseases.

The main, active ingredients in vaccines are antigens. Antigens are small bits of the bacteria or virus you are being vaccinated against. In vaccines, these antigens are weakened, inactivated (killed), or only partially used. This makes them safe and unable to cause infection. Antigens are what encourage your immune system to create antibodies to fight against future infections. Learn more about how vaccines are made and how antigens work.

Just like many foods we eat, vaccines also contain additional ingredients that each have a specific, important purpose.

These additional ingredients in vaccines are called adjuvants, stabilizers, or preservatives. They enable the vaccine to do its job. That job is to trigger a natural immune response in the body. Vaccines do this by producing antibodies that can recognize and fight off a particular antigen. The additional ingredients make vaccines effective, sterile, safe, and long-lasting. These ingredients are tested for safety and are only included in very small amounts in each vaccine. They are safe for people at these amounts. Typically, vaccines only have trace amounts of these components. They have much less than children encounter in their environment, food, and water.

Click on an ingredient to learn more about it.

Adjuvants

Adjuvants: help boost the body’s immune response to a vaccine. Without adjuvants, vaccines would be less effective and require higher doses.

Example: aluminum salts
Natural sources: drinking water, breast milk

Stabilizers

Stabilizers: help keep the vaccine effective after manufacturing by increasing its storage life. They keep the vaccine from changing when it is exposed to heat, light, or humidity.

Examples: sugar, gelatin, monosodium glutamate (MSG) and 2-phenoxy-ethanol
Natural sources: foods! (sugar, gelatin)
Vaccines containing gelatin have been approved for use by leaders of the Muslim and Jewish communities.

Preservatives

Preservatives: prevent contamination and bacterial growth in vaccine vials that hold multiple doses. The only current vaccine that uses a preservative is the multi-dose flu vaccine. Because so many people need the flu vaccine at once, it is important to transport it in vials that hold multiple doses.

Examples: thimerosal, a type of mercury, which is quickly broken down and cleared from your body.
Thimerosal is an ethylmercury which is very different from methylmercury. Methylmercury is what can build up in fish and your body. Ethylmercury leaves the body much faster.
Single-dose flu vaccines without thimerosal are also available.

Residual Ingredients

Residual Ingredients: are ingredients used in the manufacturing process of vaccines. They can remain in the final vaccine in very small amounts. They are not harmful.

Examples:

Antibiotics are used to prevent the growth of bacteria during vaccine production and storage. Antibiotics that people are often allergic to, like penicillin, are not used. Only small amounts remain in the final vaccine.
Eggs are used to grow the virus or bacteria that is used to make vaccines, including some flu vaccines. These vaccines can contain a small amount of egg proteins. Studies have shown that severe allergic reactions to this amount of egg are unlikely. It is safe for people with egg allergies to get any of the flu vaccines.
Formaldehyde is used to inactivate toxins, viruses, and bacteria in DTaP and Tdap vaccines. It is not dangerous in very small amounts, like the amounts used in vaccines. Formaldehyde is naturally found in the human body and fruit.