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Hailed as one of the ten great public health achievements of the 20th Century by the U.S. Centers for Disease Control and Prevention (CDC), vaccines can help save 2 to 3 million lives every year.

As a result of vaccinations, diseases like diphtheria have been drastically reduced; many diseases have even been eliminated. The benefits of the vaccine development process are clear: routine immunizations given to the 78.6 million individuals born in the United States over the past two decades will help prevent 322 million illnesses, 21 million hospitalizations and 732,000 deaths, according to the CDC.

Vaccines work thanks to innovations in biotechnology and chemistry. By introducing a modified or “imitation” version of a disease like polio or measles to a person’s immune system, the body is able to recognize and fight off future exposure to the disease, resulting in reduced severity of symptoms. As a result, vaccine-induced immunity works with the body’s natural defenses to help it resist and overcome disease.

Are Vaccines Safe?

Yes. To achieve and maintain vaccine safety, the U.S. Food and Drug Administration (FDA) regulates and oversees the vaccine development process.

Are vaccines tested for safety?

New vaccines undergo rigorous testing, including vaccine safety studies and licensing of the ingredients used in vaccines through a multiphase approval process that can take 10 or more years. Even after vaccine approval has been achieved, the FDA continues safety monitoring, including the occurrences of vaccine side effects.

However, during national emergencies, such as the COVID-19 Pandemic, the FDA may use a special power called Emergency Use Authorization (EUA) to allow the use of medical treatments such as vaccines that have not been fully approved yet if there’s a serious or life-threatening condition to public health.

The rules for this special power are found in a law called the Federal Food, Drug, and Cosmetic Act (FD&C Act) and declared by the head of the U.S. Department of Health and Human Services (HHS) when there’s no other good treatment available.

Although vaccines are now commonplace and have proven effective at eliminating once deadly diseases, incorrect information can spread quickly through social media, leading to concerns about vaccine side effects and vaccine ingredients.

But why are chemicals added to vaccine ingredients?

Chemical ingredients can be added to vaccines for a variety of purposes – some are added to inactivate a virus or bacteria and stabilize the vaccine, while others are added to preserve the vaccine efficacy, preventing the vaccine from losing its potency over time.

It is important to review the ingredients in vaccines with your doctor to avoid any possible vaccine allergens. For example, some individuals may have an allergy to egg protein which can be found in most flu vaccines. Discussing your individual needs with a healthcare professional can prevent unnecessary and unpleasant vaccine side effects.

Common Ingredients in Vaccines:

  • Aluminum gels/salts: Aluminum is one of the most common chemical elements in nature and is found in air, food and water. Tiny amounts of aluminum are added to some vaccines to help the body build stronger immunity against the virus in the vaccine.Aluminum additives are used in vaccines for viruses such as hepatitis A, hepatitis B, and diphtheria-tetanus-containing vaccines, among others. Health officials recommend these vaccines for babies and young children, which sometimes leads parents to question the safety of aluminum in the shots. However, babies already have a small naturally occurring amount of aluminum in their bloodstreams, about 5 nanograms (a nanogram is equal to one billionth of a gram) from infant formula or breast milk. The amount of aluminum in a vaccine is far below the amounts that babies are naturally exposed to. According to FDA, vaccines containing aluminum have a demonstrated safety profile based on more than six decades of use and are only rarely associated with vaccine side effects, such as skin irritation or swelling.
  • Antibiotics: Certain antibiotics, including neomycin, polymyxin B, streptomycin, and gentamicin, can be used in the production of some vaccines to help prevent bacterial contamination and fungus growth. For example, during the production of an influenza virus vaccine (also known as flu shots or flu jabs), antibiotics are used to reduce bacterial growth in the egg ingredients, which are not naturally sterile and could otherwise contaminate the vaccine.
  • Chicken protein: Vaccines may contain very small amounts of the culture material used to grow the virus or bacteria used in the vaccine, such as chicken egg protein. For example, the most common way that flu vaccines are made is through an egg-based manufacturing process that has been in existence for more than 70 years.
  • Formaldehyde and other preservatives: Tiny amounts of formaldehyde have long been used in the manufacture of viral and bacterial vaccines. In fact, formaldehyde is found everywhere, our bodies produce it, and we even exhale miniscule concentrations of formaldehyde in our breath. The amount of formaldehyde present in some vaccines is so small compared to the concentration that occurs naturally in the body that it does not pose a safety concern. In vaccines, formaldehyde is used to inactivate a virus before it can cause the disease the person is being vaccinated against (for example, the polio virus used to make polio vaccine) and to detoxify bacterial toxins, such as the toxin used to make the diphtheria vaccine. Formaldehyde is a common vaccine preservative also added to some vaccines to prevent the growth of bacteria or fungi that could be introduced into the vaccine during actual vaccination.
  • Sugars and other stabilizers: Sugar is sometimes used as a stabilizer to help the vaccine maintain its effectiveness during storage and transit. Vaccines are shipped all around the globe; it’s critically important that they work when needed, and don’t degrade or lose effectiveness during the heat and cold of shipping. Other stabilizers added to vaccines include lactose and amino acids such as glycine or the monosodium salt of glutamic acid, and proteins such as human serum albumin or gelatin.

Explore other Chemicals and Health topics to learn about more ways chemistry plays a vital role in keeping us healthy and safe.

Frequently Asked Questions

What are the common ingredients in vaccines and why are they used?

Vaccines often contain ingredients like aluminum salts, antibiotics, chicken protein, formaldehyde, and sugars. These ingredients serve various purposes. Aluminum salts help the body build stronger immunity against the virus in the vaccine. Antibiotics are used to prevent bacterial contamination and fungus growth during vaccine production. Chicken protein is a culture material used to grow the virus or bacteria for the vaccine. Formaldehyde is used to inactivate a virus or detoxify bacterial toxins. Sugars act as stabilizers to maintain the vaccine’s effectiveness during storage and transit.

How does the FDA ensure the safety of vaccines?

The U.S. Food and Drug Administration (FDA) regulates the development, testing, and licensing of vaccines through a rigorous multiphase approval process that can take 10 or more years. Even after approving a vaccine, the FDA continues to monitor its safety to ensure any potential side effects or issues are promptly addressed.

Why is formaldehyde in vaccines?

Formaldehyde is used in the manufacture of viral and bacterial vaccines to inactivate a virus to detoxify bacterial toxins. Preservatives like formaldehyde in vaccines are also added to prevent the growth of bacteria or fungi that could be introduced into the vaccine during actual vaccination. The amount of formaldehyde present in some vaccines is so small compared to the concentration that occurs naturally in the body that it does not pose a safety concern.

Vaccine Information Statements (VISs)

Getting a flu shot this winter? The CDC provides Vaccine Information Statements (VISs) for flu vaccine recipients. VISs explain the benefits and risks of a vaccine, what to do in case of a serious allergic reaction, and guidance on talking to your healthcare provider. For more information about the flu vaccine, visit

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