What are vaccines made of?

Short Answer

Vaccines are made up of small amounts of weakened or dead versions of bacteria, a virus, or another antigen (a foreign substance that induces an immune response), and stimulate the immune system to create antibodies that prevent future infections from the disease. Like many of the foods we eat, small amounts of additives may be mixed into the vaccine’s formula to preserve or improve its effectiveness and keep it sterile.




While all ingredients are FDA approved, sometimes a child may be sensitive to one of the components of a vaccine, and an allergic reaction may result. For this reason, you should discuss any allergies your child may have with your health-care provider.

Vaccines may include:

Preservatives and stabilizers: Since 1968, the United States Code of Federal Regulations (the CFR) has required, in general, the addition of a preservative to multi-dose vials of vaccines; and worldwide, preservatives are routinely added to multi-dose vials of vaccine. Tragic consequences have followed the use of multi-dose vials that did not contain a preservative (including deaths), and have served as the driving force for this requirement.

Thimerosal: A commonly known preservative, thimerosal, was at the center of controversy a few years ago. Thimerosal, an ethylmercury-based preservative, was phased out of vaccines in the late 1990s in an effort to reduce the overall burden of mercury from all environmental sources. Unlike the methylmercury found in the environment, however, ethylmercury is quickly excreted from the body. Today, influenza vaccine is the only vaccine that still contains thimerosal as a preservative, and there is a thimerosal-free formulation available for administration to children.

Formaldehyde may be used as an antimicrobial. Vaccines contain a small amount of formaldehyde used to inactivate viruses and bacteria. The quantity of formaldehyde in individual vaccines does not exceed one tenth of a milligram, which is considered to be safe because it is essential in human metabolism, and is required for the synthesis of amino acids. Everybody has detectible quantities of formaldehyde in their bloodstream, and there is far more naturally circulating in the body than what is contained in vaccines.


Aluminum has been used in some vaccines for over 75 years to improve the vaccine’s performance by helping to stimulate the body’s immune system to produce antibodies. Without the use of an adjuvant we would need to administer more shots in a given vaccine series or face lower immunity and less protection from the disease. Aluminum is also commonly found in food, water, infant formula, and even breast milk.

Egg protein: Some vaccines are prepared in eggs. If your child has had an allergic reaction to eggs or egg products, you should be sure to discuss this with your child’s doctor.

Antibiotics are present in some vaccines to prevent bacterial contamination during the manufacturing process.

Yeast proteins are added during the creation of hepatitis B vaccine and one brand of the human papillomavirus (HPV) vaccine (Gardasil®). Yeast proteins do not cause an allergic reaction in people who are allergic to bread products.

Gelatin is used in vaccines as a stabilizing agent, allowing small quantities of live viral vaccine to be evenly distributed throughout the container. The incidence of allergic reaction to gelatin is extremely low (1 in 2 million doses).

Some vaccines are created with human fetal cells that were obtained from two elective abortions (one in England and one in Sweden) in the early 1960s. These two sources of fetal cells have been used to make vaccines against rubella, rabies, chickenpox, and hepatitis A. These vaccines are approved for use by the Vatican and National Catholic Bioethics Center in Boston, and are not considered to be immoral by these groups.

In addition to these ingredients, you may have heard that vaccines contain products such as antifreeze and other outrageous components. This is not true. The claim of antifreeze being in vaccines comes from the use of polyethylene glycol in one brand of the flu vaccine to inactivate the virus. It is also used to purify certain vaccines. But polyethylene glycol is not antifreeze; it is just a component that is found in antifreeze, just as water is a component. Polyethylene glycol has a low toxicity,* and is used in a variety of products. It is the basis of a number of laxatives and skin creams, and is used as an irrigating solution in surgical procedures and in drug overdoses.

*Victor O. Sheftel (2000). Indirect Food Additives and Polymers: Migration and Toxicology. CRC, 1114-1116.