Many people are unaware of the problems associated with allergic reactions to vaccine components. According to the 2006 Red Book (Report of the Committee on Infectious Diseases. 2006 AAP), allergic reactions to vaccine ingredients are rare. The most common difficulties are encountered with hypersensitivities to chickens or eggs, mercury, certain antibiotics, or to gelatin.

If your child has Antibiotic Allergies:

• 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. 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.

If your child has 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). Even those with dramatic egg allergies are extremely unlikely to have an anaphylactic reaction to the MMR.
• 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.
• 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. 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.

If your child has Gelatin Allergies:

• Some of the live vaccines do contain gelatin as a stabilizing agent.
• 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.
• 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.

If your child has Mercury Allergies:

• Mercury (thimerosal) is an ingredient in several vaccines -- included in order to kill any live contaminants. In rare instances, this causes allergic reactions. It is most likely to be used for a vaccine stored in a multi-dose vial.
• All of the vaccines in the routine schedule are available in thimerosal-free forms or contain only trace amounts of thimerosal, with the exception of some inactivated influenza vaccines. There is a trace thimerosal-containing formulation of the inactivated influenza vaccine, but it is available in limited supply.
• The American Academy of Pediatrics (AAP) and the United States Public Health Service (PHS) has called for the elimination of mercury from all vaccines. Multi-dose vials require a preservative to prevent microbial contamination after the vial is opened, but manufacturers are encouraged to seek alternatives.