What Ingredients Are Used to Make Vaccines?

Vaccines are an important way to protect yourself and those around you from getting sick. 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. Getting vaccinated protects you from infection. And people around you are protected because you’re 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’re safe and nontoxic. And vaccines are important to keep you protected from dangerous infections. 

What are the different types of vaccines and their active ingredients?

Here are the main vaccine types:

• Inactivated (dead) vaccines

• Subunit and conjugate vaccines

• Live vaccines

• mRNA vaccines

Let’s take a closer look at the active ingredients in these vaccines.

Inactivated vaccines

Inactivated vaccines are made from killed viruses or bacteria. When used in a vaccine, the dead germs teach your immune system how to defend the body against the living versions. Some examples include:

• Hepatitis A

• Polio vaccine

• Most flu shots

Subunit and conjugate vaccines

Subunit and conjugate vaccines use only a specific piece of the germ — like a protein or part of the outer layer of the germ. They teach the immune system to identify an infection by recognizing that specific piece.

Examples of subunit and conjugate vaccines include:

• Hepatitis B vaccine

• HPV (human papillomavirus) vaccine

• Shingles vaccine

• Pneumococcal conjugate vaccines

• Novavax COVID vaccine

• Flublok Quadrivalent flu vaccine

Live attenuated vaccines

Live vaccines are made of living viruses or bacteria. These germs have been attenuated, meaning that they’re weaker than the normal germs. Because they’re similar to the full-strength germs, your body learns how to fight them off. But because the germs are weakened, a healthy immune system can easily stop them — so they never cause an infection.

Examples of live attenuated vaccines are:

• Measles, mumps, and rubella (MMR)

• Chicken pox (varicella)

• Rotavirus

• Nasal spray flu vaccine

mRNA vaccines

An mRNA vaccine gives the immune system a genetic blueprint for a specific part of a germ. That genetic blueprint is like an instruction manual for your immune cells to learn how to fight off the real thing if it comes along. The most common examples of mRNA vaccines are the Pfizer and Moderna COVID vaccines.

Even though they contain genetic material, mRNA vaccines don’t change your genes. They just show the body how to create an immune response if the time comes. 

What are the other ingredients in vaccines?

There are additional ingredients in vaccines, aside from the parts of the bacteria or virus. The names of some of these ingredients can be the source of alarm and confusion for people. Here’s 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 main ingredient of a vaccine alone is not enough to make lasting protection, so adjuvants are added to make the vaccine more effective. Here are some examples of adjuvants:

• Aluminum, in small amounts that scientists have found to be 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 genetic material that resembles DNA from bacteria or viruses

Preservatives

Many vaccines contain preservatives. In vaccines, preservatives prevent contamination with bacteria — which keeps them safe until they’re injected into the body.

Thimerosal is a preservative that contains mercury. 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. It’s only used in certain versions of the influenza vaccine. And trace amounts may be found in one version of the tetanus vaccine from the manufacturing process. 

Stabilizers

Stabilizers are ingredients that protect vaccines while they’re 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 to grow organisms in culture: Egg protein is an example.

• Ingredients to kill or damage active ingredients: Formaldehyde, for example, can be toxic in large amounts, but it’s safe in small amounts. 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 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.

Ingredients in common vaccines

Common questions and vaccine misconceptions