Key takeaways
It’s normal to want to understand what ingredients are included in vaccines before making a vaccination decision for yourself or your loved ones.
Vaccine ingredient lists can sometimes look technical at first glance, but each ingredient has a specific purpose, such as supporting the immune system to recognize a threat, keeping the vaccine stable, preventing contamination, or supporting the manufacturing process.
The amounts of each ingredient in a vaccine are small, and the development process is rigorously regulated.
What ingredients are used in vaccines?
Vaccines usually include a small number of ingredients, each belonging to a category with a specific purpose.
Not every vaccine contains the same ingredients. Vaccines are developed in different ways depending on the target virus or bacteria and how the vaccines are meant to work. However, vaccine ingredients generally fall into five categories:
- Antigens: The active part of the vaccine. This is what trains the immune system to recognize a specific virus or bacterium. Antigens may be a weakened pathogen (disease-causing agents such as a virus or bacteria), an inactivated pathogen, a piece of a pathogen, a toxin that has been made harmless, or instructions that help the body make a harmless protein for the immune system to recognize.
- Adjuvants: Ingredients that help your immune system respond more strongly to the vaccine. For example, some vaccines use small amounts of aluminum salts for this purpose.
- Stabilizers: Ingredients such as sugars or gelatin that help keep the vaccine effective during storage or transport.
- Preservatives: Preservatives are used to help protect vaccines from contamination. This can be important for vaccines stored in multi-dose vials, where a dose is drawn more than once. Since 2001, the preservative thimerosal has been removed from childhood vaccines in the U.S. as a precautionary measure. Research does not show any link between thimerosal in vaccines and autism or neuropsychological delays.
- Trace components: Very small residual amounts of material left over from the manufacturing process, such as formaldehyde or certain antibiotics. These are used during production and largely removed, leaving only tiny amounts in the final vaccine. Formaldehyde is used to inactivate viruses so that they don’t cause disease and to detoxify bacterial toxins. It has a long history of safe use in the manufacture of certain viral and bacterial vaccines. Certain antibiotics may be used in some vaccine production to help prevent bacterial contamination during manufacturing. The very small amounts of antibiotics contained in vaccines have not been clearly associated with severe allergic reactions.
What role do vaccine ingredients play?
Each ingredient serves a specific purpose. Looking at ingredients through that lens can make the list easier to understand. Instead of asking: “What is this?” it can help to ask: “What does this do?”
- Antigens teach the immune system what to recognize: When the immune system sees an antigen, it learns to identify a specific pathogen, such as a virus or bacterium. This helps the body build immune memory so it can respond more quickly if exposed to the real infection later.
- Adjuvants help the immune system respond more effectively: Some vaccines include adjuvants because the antigen alone may not create a strong enough immune response. Aluminum salts, for example, have been used to help boost the immune response to certain vaccines by helping the body respond more strongly to the vaccine antigen.
- Stabilizers help vaccines remain effective: Vaccines may travel through multiple stages before reaching a patient: manufacturing, quality testing, storage, shipping, and delivery at a clinic or pharmacy. Stabilizers help protect the active ingredients from changes that could reduce effectiveness, such as temperature shifts.
- Preservatives help prevent contamination: They are most relevant for multi-dose vials, where more than one dose is drawn from the same container. Each time a vial is accessed, there is a potential risk of a pathogen entering it. Preservatives help reduce that risk.
- Trace components have roles during the manufacturing process: These may include very small amounts of substances used to manufacture the vaccine. They are not needed for the vaccine to work in the body.
Are vaccine ingredients safe?
Questions about safety are often at the center of conversations about vaccine ingredients. It is important to note that vaccine safety is evaluated before approval and continues to be monitored after vaccines are in use. Learn more about how vaccines are tested for safety.
In the United States, the Food and Drug Administration (FDA) reviews data from laboratory studies, animal studies, and human clinical trials before licensing a vaccine. As part of the review, independent regulatory bodies evaluate the full vaccine formulation, meaning all ingredients are assessed together in the context of how they work as a complete vaccine, not on their own.
Ingredients are used in very small, carefully controlled amounts. For example, FDA regulations limit the amount of aluminum allowed in a vaccine dose. Formaldehyde, which may be found in tiny residual amounts in certain vaccines, has a long history of safe use in the vaccine manufacturing process.
How much aluminum is in vaccines?
Aluminum salts are used in some vaccines as adjuvants, meaning they help the immune system respond more strongly to the vaccine.
There have been claims that aluminum salts in vaccines can cause autism, other neurodevelopmental conditions, or serious health issues in children.
Most vaccines that use aluminum contain between 0.125 to 0.85 milligrams per dose. This amount is small and carefully controlled.
Aluminum is also present in everyday life, including in food and water. Adults typically ingest about 7–9 milligrams of aluminum per day, and infants receive more aluminum from diet than from vaccines during the first six months of life.
Tiny amounts of aluminum salts have been used in vaccines for decades, and studies, including a Danish study of ~1.2 million children, have found no substantial risk between tiny amounts of aluminum in early childhood vaccines and conditions such as autism, asthma, or allergies.
What are live vaccines and how do they work?
Live vaccines, also known as live-attenuated vaccines, are vaccines that use a weakened form of a virus. These pathogens have been weakened so are less likely to cause disease in people with healthy immune systems in the same way they would in their natural form.
Because live-attenuated vaccines closely mimic natural infection, they can create a strong and long-lasting immune response. Example vaccines include MMR (measles, mumps, and rubella), chickenpox, rotavirus, smallpox, and yellow fever.
Live vaccines have decades of safety and monitoring data behind them, but they are not recommended for everyone. People with certain health conditions, including those who have a weakened immune system (immunocompromised) and those who are pregnant, may be advised to receive other types of vaccines instead. A healthcare provider can help guide that decision.
What are mRNA vaccines?
Messenger ribonucleic acid (mRNA) vaccines are different from live vaccines. They do not contain a live virus but instead use laboratory-made mRNA to teach your cells to make a piece of protein (an antigen) that triggers an immune response. This immune response, which produces antibodies, is what helps protect you from getting sick from a given pathogen in the future.
How to talk to your healthcare provider about vaccine ingredients
If you have questions or concerns about vaccine ingredients, share them with your healthcare provider. A conversation with your doctor can provide the context they need to make recommendations for you based on your health history and any worries you may have.
Here are some questions you might want to consider asking at your appointment:
- Are there any vaccine ingredients I should be aware of given my allergies or health history?
- Based on my age and health history, which vaccines do you recommend I stay current on?
- Where can I find further information on the ingredients for this specific vaccine?
Remember, vaccine ingredients each serve a specific purpose. Some help the immune system recognize a threat or help strengthen the immune response. Others keep vaccines stable, prevent contamination, or support manufacturing. Ingredients are evaluated as part of the complete vaccine formulation before approval, and vaccine safety continues to be monitored after vaccines are in use.
Find out which vaccines are recommended for you by taking a quiz and book your appointment at VaxAssist by Pfizer.
Frequently
asked questions
Where can I find trusted vaccine safety resources?
Trusted resources include the CDC, FDA, VSD, VAERS, and Children’s Hospital of Philadelphia Vaccine Education Center (CHOP). These organizations provide vaccine ingredient lists, vaccine safety information, and vaccine-specific information.
How do I discuss ingredient concerns with my healthcare provider?
Start addressing your concerns about vaccine ingredients by discussing your medical history with your healthcare provider, such as any allergies or chronic health conditions, past vaccine reactions, pregnancy, weakened immune system, or medications. With this context, you can explore your vaccine options, how they work, and what ingredients they include.
How do the ingredients in mRNA vaccines differ from live vaccines?
mRNA vaccines are different from live vaccines as they do not contain a live virus. They use mRNA instructions to help the body make a protein that triggers immune recognition. Live vaccines use a weakened form of a pathogen (typically a virus or bacterium).
Do vaccine ingredients stay in your body?
Most vaccine ingredients do not remain in the body long-term. After vaccination, the immune system responds to the antigen, while other components are broken down, used by the body, or cleared through normal biological processes. Ingredients are used in carefully controlled amounts to help keep vaccines as effective and safe as possible.
Why do different vaccines contain different ingredients?
Vaccines contain different ingredients because different diseases require different approaches. Scientists consider how the immune system responds to each pathogen, who needs protection, and which vaccine approach is most effective.
What are mRNA vaccines?
mRNA vaccines are a type of vaccine that use a small piece of genetic instruction (called messenger RNA, or mRNA) to teach your cells to make a harmless piece of a virus. This prompts your immune system to build a response and recognize it in the future. Unlike live vaccines, they do not contain a live virus or weakened virus. The mRNA is temporary, does not enter the part of the cell where DNA is stored, and is broken down after it delivers its instructions.
Can people with egg allergies get vaccinated?
People with egg allergies can get any licensed recommended vaccine, such as the flu vaccine, that’s appropriate for their age. They no longer have to be watched for 30 minutes after getting the vaccine. People who have severe egg allergies should be vaccinated in a medical setting and be supervised by a healthcare provider who can recognize and manage severe allergic conditions.
More relevant articles
Keep reading
- /vaccines/education/how-do-vaccines-work
- /vaccines/education/how-to-discuss-vaccines-with-your-healthcare-provider
- /vaccines/education/vaccine-safety-and-testing
- /vaccines/education/vaccination-for-cancer-patients
References
Andersson NW, Bech Svalgaard I, Hoffmann SS, Hviid A. Aluminum-adsorbed vaccines and chronic diseases in childhood: a nationwide cohort study. Ann Intern Med. 2025;178(10):1369-1377. doi:10.7326/ANNALS-25-00997
American Academy of Pediatrics (AAP). Fact checked: aluminum in vaccines strengthen immune responses, do not cause autism, serious health issues. Reviewed December 4, 2025. Accessed June 17, 2026. https://www.aap.org/en/news-room/fact-checked/fact-checked-aluminum-in-vaccines-strengthen-immune-responses-do-not-cause-autism-serious-health-issues/
Centers for Disease Control and Prevention (CDC). About the vaccine safety datalink (VSD). Reviewed September 12, 2025. Accessed June 12, 2026. https://www.cdc.gov/vaccine-safety-systems/vsd/index.html
Centers for Disease Control and Prevention (CDC). How vaccines are developed and approved for use. August 10, 2024. Accessed July 1, 2026. https://www.cdc.gov/vaccines/basics/how-developed-approved.html
Centers for Disease Control and Prevention (CDC). Vaccines & Immunizations. Contraindications and precautions. Reviewed July 25, 2024. Accessed June 12, 2026. https://www.cdc.gov/vaccines/hcp/imz-best-practices/contraindications-precautions.html
Centers for Disease Control and Prevention (CDC). COVID-19 vaccine basics. Reviewed September 3, 2024. Accessed June 12, 2026. https://www.cdc.gov/covid/vaccines/how-they-work.html
Centers for Disease Control and Prevention (CDC). How vaccines are developed and approved for use. August 10, 2024. Accessed June 11, 2026. https://www.cdc.gov/vaccines/basics/how-developed-approved.html
Centers for Disease Control and Prevention (CDC). How vaccine safety monitoring works. Reviewed August 8, 2024. Accessed June 30, 2026. https://www.cdc.gov/vaccine-safety-systems/about/monitoring.html
Centers for Disease Control and Prevention (CDC). Thimerosal and vaccines. Reviewed October 28, 2025. June 17, 2026. https://www.cdc.gov/vaccine-safety/about/thimerosal.html
Centers for Disease Control and Prevention (CDC). Vaccine basics. Reviewed August 10, 2024. Accessed June 12, 2026. https://www.cdc.gov/vaccines/basics/index.html
Children’s Hospital of Philadelphia (CHOP) Vaccine Education Center. Vaccine ingredients: Aluminum. Reviewed June 4, 2026. Accessed June 12, 2026. https://www.chop.edu/vaccine-education-center/vaccine-safety/vaccine-ingredients/aluminum
Department of Health and Human Services (HHS). Vaccine ingredients. Reviewed April 29, 2021. Accessed June 12, 2026. https://www.hhs.gov/immunization/basics/vaccine-ingredients/index.html
Department of Health and Human Services (HHS). Vaccine types. Reviewed April 17, 2026. Accessed June 12, 2026. https://www.hhs.gov/immunization/basics/types/index.html
Food and Drug Administration (FDA). Common ingredients in FDA-approved vaccines. Reviewed March 2, 2026. Accessed June 12, 2026. https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/common-ingredients-fda-approved-vaccines
Food and Drug Administration (FDA). VAERS overview. Reviewed August 12, 2021. Accessed June 12, 2026. https://www.fda.gov/vaccines-blood-biologics/vaccine-adverse-events/vaers-overview
John Hopkins. Bloomberg School of Public Health. The science of vaccine safety in the US. February 21, 2025. Accessed July 1, 2026. https://publichealth.jhu.edu/2025/how-the-us-ensures-vaccine-safety
Johns Hopkins Medicine. Vaccines. Accessed July 1, 2026. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/vaccines
United States Environmental Protection Agency (EPA). Aluminum salts in vaccines--US perspective. Reviewed January 23, 2026. Accessed June 30, 2026. https://hero.epa.gov/reference/1988918/
World Health Organization (WHO). Vaccines and immunization: vaccine safety. Reviewed September 23, 2025. Accessed July 1, 2026. https://www.who.int/news-room/questions-and-answers/item/vaccines-and-immunization-vaccine-safety
Ying C, Megan H, Yongjie H, Yuan S. Vaccine adjuvants: current status, research and development, licensing, and future opportunities. J Mater Chem B. 2024; ; 12(17): 4118–4137. doi:10.1039/d3tb02861e.