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Immunology 101 Series: Adjuvants, Aluminum, and Gelatin! Oh My! The Scientific Scoop on Vaccine Ingredients

By Aimee Pugh-Bernard, PhD

Are the ingredients in vaccines necessary and useful? YES!

All of the ingredients within vaccines are vital and play a role in important things like helping the immune system respond, maintaining the longevity of the vaccine itself, and keeping the vaccine safe from contamination.

In the ninth installment of the Immunology 101 Series, Aimee will explain the science behind the ingredients in vaccines.

As a parent, you may want to know what ingredients are in vaccines and what each of the ingredients does. The simple answer is that the ingredients in vaccines are necessary to help the vaccine work better and create the best possible immune response. Some ingredients also help to preserve the vaccine, and others are a result of the manufacturing process.

It is also important to understand that not every component listed below is contained in every vaccine. Vaccines are made by different companies and, as a result, the ingredients can differ slightly between vaccines. It’s kind of like comparing recipes for chocolate chip cookies baked by my grandma to chocolate chip cookies made by your grandma. Both batches of cookies will be delicious but the ingredients (and sometimes amounts of the same ingredients) may differ slightly. It’s the same with vaccines. All are safe and effective even though they may have slightly different components or different amounts of the same components. Whatever the ingredient, you can be reassured that each is necessary. But just to be certain, let’s look at each ingredient individually below.

Adjuvants
The word ‘adjuvant’ is a scientific word for a substance that is used to boost or enhance the immune response to the vaccine. Basically, adjuvants allow the cells of the immune system to work better and for longer periods of time. Research on adjuvants has also shown that when adjuvants are added, less vaccine is needed to yield a good response. Right now, the main adjuvant used in vaccines given in the United States is aluminum salts or aluminum potassium sulfate (aka ‘alum’) to be precise.

Aluminum
Aluminum is a naturally occurring element. It is found in plants, soil, water and air. We are all exposed to aluminum every day. In fact, infants ingest aluminum at every feeding in breast milk and formula. Immunologists (scientists like me who study the immune system) have found that adjuvants are incredibly helpful at enhancing the immune response to vaccines. Alum (the abbreviated name for aluminum potassium sulfate) is used as an adjuvant in some vaccines because it boosts the immune response. Alum results in a slower release of antigen from the injection site, which increases the time of exposure (from days to weeks) giving the immune system a longer time to respond. A longer response time leads to enhanced or better protection.

Antibiotics
Antibiotics are commonly used medicines that kill bacteria (not viruses!). Antibiotics are included in some vaccines to prevent bacterial growth during the manufacturing process. The antibiotics used (separately) in some vaccines vary by manufacturer and include neomycin, gentamicin, polymyxin B, or streptomycin. Rest assured that the amount included in each vaccine is miniscule. Some people have raised concerns that these antibiotics might cause an allergic reaction. However, extensive research shows it is unlikely that the antibiotics used in vaccines would cause an allergic reaction. Allergies to antibiotics typically occur in response to other types of antibiotics, such as penicillin and its derivatives or sulfa-based drugs that are not included in vaccines. The miniscule amounts and the types of antibiotics included in vaccines make it highly unlikely that a severe allergic reaction would result from immunization.

Eggs
Why are eggs listed as an ingredient in some vaccines? The answer is simple: some vaccines that protect us from certain viruses, such as influenza and yellow fever, include the use of eggs in the manufacturing process. You may not know this, but outside of their normal hosts, like humans, viruses are very difficult to grow! Every virus has a preferred host, and even more specifically, a preferred cell type. As an example, the influenza virus grows very well in the cells of the respiratory tract and lungs of humans but does not grow well in any of the cells that scientists use in laboratories. This makes it very difficult to grow the virus to make vaccines. Fortunately scientists have found a cell type that these viruses like to grow in – chicken eggs. As a result, scientists grow the influenza virus and yellow fever virus in chicken eggs. Once there is a sufficient amount of virus grown in the eggs, scientists remove the virus from the eggs to make the vaccine.

Although the removal process works very well, it is very difficult to remove 100% of the egg. So, just to be safe, scientists and medical doctors recommend that people with egg allergies do not receive the yellow fever vaccine. Fortunately, the egg removal process for the influenza vaccine has recently been improved so that even people with egg allergies can now safely receive the influenza vaccine. Again, just to be safe, it is recommended that anyone with an egg allergy stay at their doctor’s office for ~30 minutes after receiving the vaccine to watch for signs of a reaction.

Formaldehyde
Did you know that formaldehyde is produced naturally in the human body? For example, formaldehyde is involved in the production of amino acids, which are the building blocks for proteins. Proteins are essential for every aspect of life. Now that you know formaldehyde is a natural product it is likely not as concerning to find out that extremely small quantities of formaldehyde may be found in some current vaccines as a result of the manufacturing process. Formaldehyde is used to inactivate some of the viruses (polio) and bacterial toxins (diphtheria) within vaccines. To be more specific, formaldehyde is used to break apart the pathogens (e.g. polio virus and the bacterial toxins produced by the diphtheria bacteria) so that they will no longer cause disease but still allow the immune system to respond and to be trained against them for future immunity.

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Thimerosal
Thimerosal is a preservative that contains a form of mercury called ethylmercury. I know, you are now thinking about the Mad Hatter….keep reading to learn more and breathe a sigh of relief. In the past, it was used in several vaccines as a preservative to prevent bacterial or fungal contamination. However, since 1997, thimerosal has not been used as a preservative in any vaccine other than the influenza vaccine and even this varies by manufacturer (some manufacturers use it as a preservative and others do not).

Keep in mind that years of research have shown that the small amount of thimerosal found in the influenza vaccine has a record of safe and effective use. Additionally, for those of you that desire a small chemistry lesson, ethylmercury is broken down and excreted rapidly in the human body. This means that it is highly unlikely to accumulate and cause damage.

To be absolutely clear, ethylmercury is a different type of mercury than most of you are familiar with—methyl mercury. When we think of the mercury that naturally accumulates in fish, such as tuna, it is most often methyl mercury. The methyl mercury that is consumed by eating seafood is more easily absorbed and stays in the body longer, making it much more toxic than the very tiny amount of ethyl mercury used in some vaccines. In fact, you get more than three times as much ethyl mercury eating a can of tuna!

Gelatin
Another product associated with food (watch it wiggle, see it jiggle – ring a bell?) that is included in some vaccines is gelatin. Gelatin is used in some vaccines as a stabilizer. A stabilizer is an ingredient that keeps the vaccine in an unchanging and usable form when exposed to extreme conditions like heat or freeze-drying. People who are allergic to gelatin should not receive vaccines that contain gelatin. This also varies by manufacturer so it would be best to ask your healthcare professional to check with the vaccine manufacturer.

Take home message
Vaccines are given to otherwise healthy people to prevent disease, and as such undergo intense scrutiny to be deemed safe and effective. All of the ingredients found in vaccines are necessary and serve a purpose. Nothing is added to vaccines that is unnecessary or harmful. We need to keep in mind that vaccines have contributed to a significant reduction in many childhood diseases, including, but not limited to, diphtheria, polio, measles, and whooping cough. Before vaccines against these deadly diseases were in existence thousands of children died each year.

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