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.

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 is a hot issue right now and has relevance for all newborns. This controversy has led to new (July 7, 1999) guidelines from the American Academy of Pediatrics (AAP) and the United States Public Health Service (PHS) that call for removing mercury in all forms from all vaccines.

Allergic reactions to vaccine components are another important issue. 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 chicken or eggs, mercury, certain antibiotics, or to gelatin.

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.

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.