Hidden Ingredients in Vaccines

You may be aware of problems associated with some of the components used in making vaccines, such as mercury. But what about hidden ingredients in vaccines?


Dear Dr. Greene, I read on the vaccine Internet site that you should not vaccinate for MMR (measles-mumps-rubella) if your child has an egg allergy. I found out that my 17-month baby girl gets a rash from egg whites. What kind of problems can occur when she receives the MMR vaccine? Should she not have it? Is there an alternative? Thanks for your time.
Telluride, Colorado

Dr. Greene’s Answer:

Many people are unaware of the problems associated with some of the components used in making vaccines (aside from the infectious agent itself). Potential toxicity from mercury in vaccines has been a hot issue and has relevance for all newborns. This controversy led to guidelines on July 7, 1999 from the American Academy of Pediatrics (AAP) and the United States Public Health Service (PHS) that called for removing mercury in all forms from all vaccines. But what about other hidden ingredients in vaccines?

Allergic reactions to vaccine components are another important issue. According to the 2012 Red Book (Report of the Committee on Infectious Diseases. 2012 AAP), allergic reactions to vaccine ingredients are rare. The most common difficulties are encountered with hypersensitivities to chicken or eggs, mercury, certain antibiotics, or to gelatin.

Hidden Ingredients in Vaccines: Chicken and Egg Allergies

The current measles-mumps-rubella vaccine (MMR) does not contain a significant amount of egg proteins (but two other vaccines do). As recently as 1994, the AAP recommended skin testing of all children with severe egg allergies before they received the MMR. This is no longer necessary. Even those with dramatic egg allergies are extremely unlikely to have an anaphylactic reaction to the MMR. The benefits of the vaccine far outweigh the risks.

Most people don’t know that the influenza vaccine (“flu shot“) contains egg protein. People who react to eggs, chicken, or chicken feathers with systemic symptoms (a drop in blood pressure, significant wheezing, difficulty breathing, or generalized hives) generally should not get the flu vaccine. Localized or less severe reactions (such as a mild rash) to feathers or eggs are not a reason to forgo the vaccine. Allergy to duck meat or duck feathers is not a reason to hold back on any vaccine.

The yellow fever vaccine also contains egg protein. Yellow fever is still a major problem for people living in or traveling to tropical South America or Africa. This vaccine can be very important. Thus, rather than skipping it, most candidates for the vaccine who have a suspected allergy should get a series of two skin tests with the vaccine. If both tests are fine, proceed with the vaccine. If either test shows a reaction, a process of desensitization is begun. Similar to allergy shots, a series of tiny doses of vaccine are given to reduce the risk of reaction. (CDC.gov/mmwr/preview/mmwrhtml/rr5907a1.htm)

Hidden Ingredients in Vaccines: Antibiotic Allergies

Several vaccines contain small amounts of antibiotics. Both types of polio vaccine include streptomycin, neomycin, and polymyxin B (also found in Polysporin, Neosporin, and Betadine Plus topical ointments). The MMR and the varicella vaccine have trace amounts of neomycin (found in Neosporin). Most allergic reactions to these antibiotics are nothing more than mild skin rashes. However, if your child has a severe allergy with systemic symptoms to these or related antibiotics, you should avoid these vaccines.

No vaccine contains penicillin or penicillin-related antibiotics. This type of allergy is not a reason to miss any vaccine.

Hidden Ingredients in Vaccines: Gelatin Allergies

With added sugar, flavoring, and coloring, gelatin is a popular dessert. It is also used as a thickener in soups, candies, ice creams, marshmallows and many other foods (not jelly, by the way, which uses pectin, a natural plant substance). Gelatin is used in cosmetics and in many pharmacy products including ointments, lozenges, capsules, and vaccines.

Some of the live vaccines do contain gelatin as a stabilizing agent. Gelatin is an animal protein substance made from collagen obtained by boiling animal skins, hides, bones, and other tissues after pretreatment with alkali or acid.

Gelatin is an ingredient in MMR, varicella, and yellow fever vaccines. People with severe allergies to gelatin should consider skin testing prior to receiving a gelatin-containing vaccine. The problem is that most gelatins in foods come from boiled cows, while the gelatin used in vaccines is from boiled pigs. People may not know that they are allergic to pig gelatin.

Hidden Ingredients in Vaccines: Mercury Allergies

Mercury (thimerosal) is an ingredient in several vaccines — included in order to kill any live contaminants. It is most likely to be used for a vaccine stored in a multi-dose vial. In rare instances, this causes allergic reactions. At much higher doses, mercury is a known cause of irreversible nerve and brain damage, especially before birth and in the first 6 months of life.

Mercury was responsible for the first known epidemic of cerebral palsy from a toxin when it was dumped into Minamata Bay in Japan in the 1950’s by a vinyl plastics factory. Might it also cause mercury toxicity in children who frequently get mercury-containing vaccines? This has long been a concern with the gamma globulin shot used to prevent Hepatitis A in travelers. Where practical, the Hepatitis A vaccine is a safer and more effective alternative that does not contain mercury. Still, getting a shot of gamma globulin is far better than getting hepatitis.

In the United States, all of the vaccines now in the routine schedule are available in thimerosal-free forms. Some forms of the influenza vaccine contain small amounts of thimerosal (a mercury-based preservative), but the AAP contends that the known benefits of the vaccine outweigh the hypothetical risk of small amounts of thimerosal. There are forms of the influenza vaccine that do not contain mercury (vaccines.procon.org).

The vaccination of children in much of the world will continue to require the use of multi-dose vials for reasons of cost and storage capacity. Vaccines in multi-dose vials are more likely to contain thimerosal as a preservative.

Immunizations Save Lives

Immunizations remain one of the greatest discoveries in human history, having saved innumerable lives and prevented measureless suffering. Available vaccines continue to be improved, and vaccine schedules continue to be refined. I strongly support the immunization of children and I agree with US Surgeon General David Satcher’s July 7, 1999 statement in the midst of this mercury controversy.

To our Telluride reader:

Although egg protein in the MMR is no longer a big problem, if your child has severe allergies with systemic symptoms, whatever the cause, it pays to become familiar with the hidden ingredients found in products of all kinds. Thanks for asking about this important topic.

Last medical review on: May 25, 2009
About the Author
Photo of Alan Greene MD
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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Recent Comments

Those aren’t hidden ingredients, they say those all on the CDC website……