FDA answers questions about common ingredients in U.S. vaccines

The vast majority of the more than 1 billion doses of vaccines manufactured worldwide each year are given to healthy babies, children and adults.

Thus, it is critical that vaccines be demonstrated to be safe and effective. FDA demands that vaccines undergo a rigorous and extensive development program in the laboratory, as well as in animal studies and human clinical trials, to determine their safety and effectiveness.

Prior to licensure, as part of FDA’s review, FDA takes all the ingredients into account, including the active ingredients as well as other substances. After FDA approves a vaccine, FDA and CDC continuously monitor its safety.

Why is aluminum in some vaccines?
Aluminum salts are incorporated into some vaccine formulations as an adjuvant to enhance the immune response in the vaccinated individual. The aluminum salts in some U.S. licensed vaccines are aluminum hydroxide, aluminum phosphate, alum (potassium aluminum sulfate) or mixed aluminum salts.

For example: aluminum salts are used in DTaP vaccines, the pneumococcal conjugate vaccine, and hepatitis B vaccines.

Aluminum adjuvant containing vaccines have a demonstrated safety profile of over six decades of use and have only uncommonly been associated with severe local reactions. Of note, the most common source of exposure to aluminum is from eating food or drinking water.

Are other adjuvants used in U.S. vaccines?
Yes, there is one other adjuvant used in one U.S. licensed vaccine. Cervarix, a vaccine licensed by FDA on Oct. 16 to prevent cervical cancer caused by human papillomavirus types 16 and 18, includes AS04 in its formulation. AS04 is a combination of aluminum hydroxide and monophosphoryl lipid A (MPL). MPL is a purified fat-like substance.

How does FDA evaluate adjuvants for safety and efficacy?
When evaluating a vaccine for safety and efficacy, FDA considers adjuvants as a component of the vaccine; they are not licensed separately.

Why are antibiotics in some vaccines?
Certain antibiotics may be used in some vaccine production to help prevent bacterial contamination during manufacturing. As a result, small amounts of antibiotics may be present in some vaccines.

Because some antibiotics can cause severe allergic reactions in those children allergic to them (like hives, swelling at the back of the throat, and low blood pressure), some parents are concerned that antibiotics contained in vaccines might be harmful. However, antibiotics most likely to cause severe allergic reactions (e.g., penicillins, cephalosporins and sulfa drugs) are not used in vaccine production, and therefore are not contained in vaccines.

Examples of antibiotics used during vaccine manufacture include neomycin, polymyxin B, streptomycin and gentamicin. Some antibiotics used in vaccine production are present in the vaccine, either in very small amounts or they are undetectable.

For example, antibiotics are used in some production methods for making inactivated influenza virus vaccines. They are used to reduce bacterial growth in eggs during processing steps, because eggs are not sterile products.

The antibiotics that are used are reduced to very small or undetectable amounts during subsequent purification steps. The very small amounts of antibiotics contained in vaccines have not been clearly associated with severe allergic reactions.

Why is formaldehyde in some vaccines?
Formaldehyde has a long history of use in the manufacture of certain viral and bacterial vaccines. It is used to inactivate viruses (e.g., influenza, polio) and to detoxify bacterial toxins, such as the toxin used to make diphtheria vaccine.

Formaldehyde is diluted during the manufacturing process, but residual quantities of formaldehyde may be found in some current vaccines.

The average quantity of formaldehyde to which a young infant could be exposed to at one time through vaccines is very small and is considered to be safe. Although high concentrations of formaldehyde can damage DNA (the building block of genes) and cause cancerous changes in cells in the laboratory, formaldehyde is an essential component in human metabolism and is required for the synthesis of DNA and amino acids (the building blocks of protein).

Therefore, all humans have detectable quantities of natural formaldehyde in their circulation. In addition, quantities of formaldehyde at least 600-fold greater than that contained in vaccines have been found to be safe in animals.

Why are sugars, amino acids, and proteins added to some vaccines?
These materials may be added as stabilizers. They help protect the vaccine from adverse conditions such as the freeze-drying process, for those vaccines that are freeze dried.

Stabilizers added to vaccines include: sugars such as sucrose and lactose; amino acids such as glycine or the monosodium salt of glutamic acid; and proteins such as human serum albumin or gelatin. Sugars, amino acids and proteins are not unique to vaccines and are encountered in everyday life in the diet and are components that are in the body naturally.

Why are there preservatives in some vaccines?
Preservatives are added to vaccine formulations filled into multi-dose vials to prevent the growth of bacteria or fungi that may be introduced into the vaccine during its use, e.g., repeated puncture of the vaccine vial.

Why is fetal calf/bovine serum in some vaccines?
In the manufacture of viral vaccines, the virus may be grown in cells. These cells need a source of nutrition, which in some instances may be provided by fetal bovine serum.