HomeHealth TopicVaccines

What Ingredients Make Up Vaccines?

Michael Dreis, MDSophie Vergnaud, MD
Written by Michael Dreis, MD | Reviewed by Sophie Vergnaud, MD
Published on May 24, 2021

Key takeaways:

  • Vaccines contain parts of killed germs, parts of living germs, or weakened versions of germs that teach your body how to fight those germs off.

  • Vaccines have some ingredients that keep them preserved and that strengthen your body’s response to the vaccine.

  • For the most part, vaccines are very safe. They can cause some complications, but these are rare.

Close-up of a doctor preparing a syringe with a vaccine while wearing a blue medical face mask.
CreativeDJ/E+ via Getty Images

Why trust us

Michael Dreis, MD, is a practicing physician. He received his Doctor of Medicine from the University of Wisconsin–Madison, and finished training in emergency medicine at Henry Ford Hospital in Detroit, MI. He practices medicine in Milwaukee, WI, where he teaches medical students and medical residents. He considers providing a clear explanation of medicine to be one of the most important parts of caring for people.

Dr. Dreis enjoys searching through scientific studies, society practice guidelines, and government websites, including those of the Centers for Disease Control and Prevention (CDC) and other trusted organizations, to find accurate and meaningful answers to the big questions people have about their health.

Basics

Wondering what’s in a vaccine? Vaccines are important for your health and the health of others. They are medicines that contain either a living or dead germ — the active ingredient — that teaches your immune system to fight off an infection before it has a chance to make you sick. Once vaccinated, you are better protected from infection, and people around you are protected because you are less likely to spread infection to them. 

Vaccines also contain ingredients that strengthen the immune response, prevent the vaccine from getting contaminated, and help it last until you can get it into your body. 

It’s understandable that people worry about vaccine ingredients. With names like “inactivated toxins” or “preservatives,” they sound like things you might not want to put in your body. But vaccine ingredients undergo thorough testing to make sure they are safe and nontoxic, and vaccines are important to keep you protected from dangerous infections. Read on to find out more.

Are vaccines alive or dead?

Vaccines fall into three major types:

  1. Live vaccines

  2. Dead vaccines

  3. mRNA vaccines

Live vaccines are made of living viruses or bacteria that are weaker than the normal germs that cause infections. They make a strong immune response because they’re similar to normal germs, but they don’t cause infection because they’re weakened. 

Dead vaccines are made with either killed viruses or bacteria or small parts of them. When used in a vaccine, these dead pieces of germs teach your immune system to defend the body against the living version of the germs.

Unlike the other two types, mRNA vaccines are neither live nor dead. They use new technology to deliver genetic instructions to the body for how to build its defense to a given germ.

Inactive vaccines

Inactive vaccines are made of either dead viruses or bacteria or small parts of viruses or bacteria that teach your immune system to target the germs before they cause infection. Here are some examples:

  • The tetanus shot contains tetanus that has been modified in the lab and isn’t harmful to the body. 

  • Inactivated flu vaccines can be made from a dead influenza virus or small parts of dead influenza viruses.

  • The hepatitis A vaccine is made using a dead virus.

  • The hepatitis B vaccine is made of parts of the virus (molecules on its surface). 

  • The COVID-19 vaccines are all inactive. They are made with either special genetic instructions called messenger RNA (mRNA) (Pfizer and Moderna) or an inactive virus that is different from the COVID-19 virus (Johnson & Johnson and AstraZeneca). 

Live attenuated vaccines

Live vaccines are made of living viruses or bacteria. These germs have been attenuated, meaning that they are weaker than the normal germs. Because they are similar to the dangerous germs, your body learns how to fight them off. Because the germs are weakened, your body can easily stop them — so they never cause an infection.

Examples of live attenuated vaccines are:

  • Measles, mumps, and rubella (MMR)

  • Chicken pox (varicella)

  • Live influenza vaccines

  • Tuberculosis vaccine (BGG)

  • Typhoid vaccine

  • Polio vaccine

mRNA vaccines

An mRNA vaccine is a vaccine that delivers a genetic blueprint for a specific part of a germ to the cells of the immune system. In the case of the Pfizer and Moderna COVID-19 vaccines, the mRNA delivers instructions for recognizing and mounting a defense against a surface molecule of SARS-CoV-2, the virus that causes COVID-19. Your body then uses these instructions to teach itself to fight off the disease before you get exposed to the virus. Learn more here.

No, vaccines will not alter your DNA. The mRNA vaccines don’t make any changes to your genes. They just show the cells the information they need to know to mount a response. The other COVID-19 vaccines, such as the Johnson & Johnson vaccine, are made from a killed virus that is different from SARS-CoV-2. They also deliver a blueprint of information to your body, similar to how mRNA vaccines work. These vaccines also do not change your DNA.

Will a vaccine alter my DNA?

No, vaccines will not alter your DNA. The mRNA vaccines don’t make any changes to your genes. They just show the cells the information they need to know to mount a response. The other COVID-19 vaccines, such as the Johnson & Johnson vaccine, are made from a killed virus that is different from SARS-CoV-2. They also deliver a blueprint of information to your body, similar to how mRNA vaccines work. These vaccines also do not change your DNA.

Are there any harmful ingredients in vaccines?

There are extra ingredients in vaccines, aside from the main active ingredient. The names of some of these ingredients can be the source of alarm and confusion for people. Here’s information about the other ingredients that go into vaccines, why they’re used, and what you need to know about their safety

Adjuvants

Adjuvants are vaccine ingredients that stimulate your immune system to make a stronger immune response. Sometimes, the active ingredient of a vaccine alone is not enough to make lasting protection, so adjuvants are added to make the vaccine more effective. Some examples of adjuvants are:

  • Aluminum, a common substance in the environment (after lots of testing, scientists have found that the small amounts of aluminum used in vaccines are safe)

  • Squalene, a substance naturally found in skin oil

  • Monophosphoryl lipid A, a substance found on the surface of bacteria 

  • Chilean soap bark tree extract

  • Lab-made fake DNA that resembles DNA from bacteria or viruses

Preservatives

Many vaccines contain preservatives. This might sound alarming, especially if you are concerned about preservatives in your food. In vaccines, preservatives prevent contamination with bacteria — which keeps them safe until they are injected into the body.

Thimerosal is a preservative that contains mercury. If that sounds worrying, it may help to know that thimerosal is different from the toxic mercury found in the environment, such as that in fish. Studies have shown that thimerosal is safe when used in vaccines, but it’s only used in some multidose vials of the influenza vaccine and a certain tetanus vaccine. It’s easy to avoid if you are worried about it.

Stabilizers

Stabilizers are ingredients that protect vaccines while they are stored and transported. These are common, nontoxic ingredients, like sugars and gelatin.

Residual materials

Vaccines have trace amounts of leftover ingredients from the process of making the vaccine. Examples of these include:

  • Ingredients used to grow organisms in culture, such as egg protein.

  • Ingredients that can kill or damage active ingredients, such as formaldehyde. Formaldehyde can be toxic in large amounts, but it is safe in small amounts. In fact, your body even makes small amounts of formaldehyde naturally, which it breaks down. The amount of formaldehyde in vaccines is tiny compared with the natural amount of formaldehyde in your body, so it doesn’t put you at risk of health problems.

  • Antibiotics used to kill bacteria and prevent contamination. The antibiotics in vaccines are not the same antibiotics that people take normally. Because of this, it’s rare for people to be allergic to these antibiotics.

Are vaccine ingredients toxic?

Some vaccine ingredients can be toxic in large amounts. The same is true for all medications that we take. In fact, most things consumed in large amounts are toxic. The levels of additional ingredients in vaccines are tiny. Vaccines are proven to be nontoxic through thorough safety testing before the CDC and FDA approve them.

Ingredients in common vaccines

What are the ingredients of the COVID-19 vaccine?

The COVID-19 vaccines generally contain:

  • mRNA or an inactive virus containing SARS-CoV-2 genetic information that triggers the body’s immune response

  • A fat solution for storage and protection

  • Sugars used as stabilizers

What are the ingredients of the flu vaccine?

There is no single recipe for flu vaccines, but they all contain a similar set of ingredients, such as:

  • Killed influenza virus or a small part of it

  • Egg protein in some

  • Sugars

  • Salt solutions

  • Thimerosal in small amounts in some

  • Small amounts of formaldehyde in some

  • Small amounts of antibiotics

What are the ingredients of the TDaP vaccine?

The tetanus, diphtheria, and pertussis (TDaP) vaccines generally contain:

  • An inactive tetanus toxoid

  • Small parts of diphtheria bacteria

  • Small parts of pertussis bacteria (whooping cough)

  • Aluminum

  • Antibiotics in small amounts

  • Formaldehyde in small amounts

What are the ingredients of the MMR vaccine?

The MMR vaccine contains:

  • Live, weakened versions of measles, mumps, and rubella viruses

  • Sugars

  • Antibiotics in small amounts

What are the ingredients of the HPV vaccine?

The human papillomavirus (HPV) vaccine contains:

  • Small parts of HPV viruses

  • Aluminum in small amounts

  • Salt solutions

  • Yeast proteins left over from the manufacturing process

Common concerns

Are vaccines made with fetal development tissue?

Some vaccines are made using cells that once came from fetal tissue. Many years ago, scientists got some cells from fetal tissue, and they have grown the cells in the lab using that tissue ever since. Some of these lab-grown cells are used to make certain vaccines. For example, the weakened viruses for the varicella vaccine, the rubella part of the MMR vaccine, and some COVID-19 vaccines are grown in these cells. The final product doesn’t have any of the fetal tissue in it because, during the manufacturing process, the cells are removed from the vaccine.

Do vaccines really contain mercury?

Thimerosal is a preservative used in some vaccines which is made of mercury. This is a different type of mercury than that which is found in the environment, such as in fish. Your body is able to get rid of the mercury in thimerosal much faster than it can remove other types of mercury. Even so, it’s used in very small amounts and only in specific vaccines, such as multidose vials of influenza vaccine, which need more preservatives because the vials are used over and over to deliver a dose to different people.

Are vaccines completely safe?

Vaccines undergo rigorous testing to make sure they are safe for the general population. Rarely, people can have serious allergic reactions to vaccines, but this is not the norm. Certain people shouldn’t get certain vaccines, such as people who are immunocompromised. For most people, vaccines are a totally safe way to protect yourself from potentially serious infections.

References

Centers for Disease Control and Prevention. (2015). Epidemiology and prevention of vaccine preventable diseases.

Centers for Disease Control and Prevention. (2019). Why vaccinate.

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Centers for Disease Control and Prevention. (2019). What's in vaccines? 

Centers for Disease Control and Prevention. (2020). Vaccine excipient summary.

Centers for Disease Control and Prevention. (2020). Adjuvants and vaccines

Centers for Disease Control and Prevention. (2021). Understanding mRNA COVID-19 vaccines.

Centers for Disease Control and Prevention. (2021). Understanding viral vector COVID-19 vaccines.

Children's Hospital of Philadelphia. (2021). Vaccine ingredients — fetal cells.

Mitkus, R. J., et al. (2011). Updated aluminum pharmacokinetics following infant exposures through diet and vaccination. Vaccine.

Pardi, N., et al. (2018). mRNA vaccines — a new era in vaccinology. Nature Reviews: Drug Discovery.

U.S. Food and Drug Administration. (1995). Havrix package insert.

U.S. Food and Drug Administration. (2018). Recombivax HB package insert.

U.S. Food and Drug Administration. (2018). Thimerosal and vaccines.

U.S. Food and Drug Administration. (2019). Common ingredients in U.S. licensed vaccines.

U.S. Food and Drug Administration. (2021). Emergency use authorization (EUA) of the Pfizer–BioNTech COVID-19 vaccine to prevent coronavirus disease 2019 (COVID-19) in individuals 16 and older.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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