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Vaccine 101: What’s in there?


As we continue Vaccine 101 we move from history to the recipe for a vaccine. Throughout our lives we eat food, drink beverages, and use products on our bodies and around our homes. We do not always know what these things are made of, but we ingest them and use them anyways. Of these foods and products, many people have expressed concerns about what is being injected into their bodies when they get a vaccination. Much like a recipe for brownies, the ingredients that go into a vaccine all serve a specific purpose. But what exactly are these ingredients? What is their purpose?

Syringe and vaccine. Image Credit: Flickr via NIH-NIAID

Let’s say you get the vaccine for the virus that causes chickenpox, how does this protect you from chickenpox? Ingredients in the vaccine are recognized by your immune system and trigger a protective immune response. This response is what allows your body to recognize, and protect against, later exposure to the chickenpox virus. Think of it like trying to find someone in a crowd when you don’t know what they look like, but then I give you a picture so you can more easily find them. Vaccination gives your immune system a “picture” of a virus or bacteria. Your immune system can recognize it and respond quickly when that virus or bacteria enters your body, destroying it before it can cause disease.

Antigens and Adjuvants

Brownies. Image Credit: Flickr via Saaleha Bamjee

Antigens are the ingredient responsible for creating this immune response. Antigens are derived from the disease-causing organism that the vaccine is targeting. The antigen is the “picture” the immune response gets. An antigen can be a specific part of the disease-causing organism, like the DNA or RNA, or the whole organism. The ones that use whole organisms can be a weakened version of the live virus or a killed, sometimes referred to as inactivated, version. For example, the chickenpox vaccine uses a weakened version of the live virus.

An adjuvant is added to the vaccine to help enhance, accelerate, and prolong the immune response started by the antigen. A common adjuvant is aluminum, this helps to direct how the immune system responds to the antigens making it more effective. But why would you want to allow aluminum to be injected into your body? Aluminum exposure is an everyday occurrence for us. We find it in our food, medicines and everyday items like a soda can. We intake around 10-15mg daily, with most of it being removed by our kidneys. Even infants ingest around 7mg through breast milk in the first six months of life, compared to 4.4mg of aluminum making up the vaccines administered over the first six months of life. Adjuvants are important components of a functional and effective vaccine, and common ones like aluminum pose no risk to our health.

Aluminum Cans. Image Credit: Flickr via Ishikawa Ken.

Antibiotics and Preservatives

While not as tasty as adding a stick of butter to a brownie recipe, antibiotics are a necessary ingredient in vaccines to prevent bacterial contamination during manufacturing.  Antibiotics like streptomycin can be found in miniscule amounts in vaccines to prevent contamination during vaccine manufacturing, with most being removed during the purification process. After the purification process vaccines are sealed in sterile containers and are not at risk for contamination. Because some antibiotics, such as penicillin, are known to cause allergic reactions, manufacturers avoid using them in vaccines to make them as safe for everyone as possible.

Preservatives are another ingredient to help in the fight against bacterial contamination as well as fungal contamination. When talking about preservatives, many people mention thimerosal. Thimerosal is a mercury-containing preservative surrounded in controversy. While many claim it is harmful when added to vaccines, scientific research studies have shown no link between thimerosal and harmful effects. However, in 1999 health service agencies and vaccine manufacturers agreed to reduce or eliminate its use in vaccines as a precautionary measure.  

Currently, the most commonly used preservative is phenoxyethanol, which is also found in cosmetics and baby care products. Antibiotics and preservatives ensure that your vaccine remains uncontaminated from foreign ingredients. After all you wouldn’t want someone adding hot sauce unexpectedly to your brownies. This is incredibly important to maintaining integrity and safety of vaccines.


We have our ingredients to create a proper immune response and to stave off unwanted contaminants, so what’s next? For a vaccine to be useful it has to be stable, meaning it can withstand exposure to heat, acidic conditions, humidity, and light. For such a complex task, there are many simple ingredients that act as stabilizers.  This includes common ingredients in

Sugar cubes. Image Credit: Flickr via Michael Allen Smith.

your home like the sugar sucrose that you use in delicious brownies or proteins like gelatin used in the Jell-o you may love or hate. These all play an important role especially when a vaccine is needed in areas without reliable refrigeration and extreme environments with low or high humidity, it must remain stable to be effective. Keeping vaccines stable is essential for promoting global health when vaccination is needed in third world countries.


Last but not least we come to formaldehyde, which has a long history of use in vaccines (check out my previous post to learn more about vaccine history!). Formaldehyde is responsible for inactivating viruses (polio vaccine), and to detoxify bacterial toxins (diphtheria vaccine) so they can not cause disease. If formaldehyde can inactivate viruses why would you be ok putting it in your own body? Formaldehyde actually occurs naturally and is produced by our bodies for important life processes. Vaccines that contain formaldehyde have 0.02mg or less, while a two month old baby can have up to 1.1mg circulating in their body at a given time. Formaldehyde is even found in the environment from building materials to household products. Most of the formaldehyde that goes into making a vaccine is removed during the purification process, resulting in the low amounts left behind. The use of formaldehyde allowed for essential vaccines, like the polio vaccine, to be made and it continues to play a critical role in the vaccine recipe.

While every vaccine may differ in the specific ingredients used to make it, these ingredients all come together to create the final product of a safe and effective vaccine. Do not let a list of ingredients scare you. Instead, seek to understand what these ingredients are and what role they play. They may never be as delicious as a pan of fresh brownies, but vaccines allow us to protect ourselves and others from life threatening diseases, even leading to disease eradication like smallpox. Tune in for my next post to learn why everyone should be vaccinated!

About the Author

10659344_10200100310786746_7394532827731756991_nA native Virginian (GO HOKIES!), Caitlin Reeves is a PhD candidate in the Microbiology department studying attachment of the human respiratory pathogen Mycoplasma pneumoniae to its human host. Outside of the lab she can be found planning events for UGA’s Women in Science (WiSci) organization, snuggling with her labradoodle Sherlock, or playing video games despite being a 26 year old “adult”.

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