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Vaccine Allergy is Rare
DEAR DR.PAUL: My son is allergic to eggs. I was told that he is allergic to vaccines. Is this true?
DR.PAUL ANSWERS: Your question brings up a few very important points. First, what is the difference between an allergy and a side effect? As with any medication, vaccines can have side effects such as fever, rash or local redness or swelling. This is not an allergy. An allergy is when the body reacts to a specific substance. An allergic reaction can be a rash, shortness of breath or swelling of the face, and these, almost immediately, or within an hour after the injection. As an example, the MMR (Measles, Mumps, Rubella) vaccine can cause a rash that occurs 7-10 days after the infection. This is not an allergic reaction. This is a side effect of the MMR vaccine itself.
What about egg allergy and vaccine allergy? The link between the two is that some vaccinations, including the MMR and Influenza vaccines are made using chicken egg or related substances. In theory, if one is allergic to eggs, then one may be allergic to egg-based vaccines. This is what we thought years ago and as a result, many egg-allergic children automatically did not receive the MMR vaccine because of this fear. However, allergy tests can be performed on any vaccine. So, to be sure, doctors can perform an allergy test for the MMR vaccine itself. If, based on the allergy test, an egg-allergic child is not allergic to the MMR vaccine, he or she receives the MMR vaccine without any problem. After years of this approach, it was realized that very, very few egg-allergic children were actually allergic to the MMR vaccine. As a result, current expert recommendations are to go ahead an vaccinate egg-allergic children with the MMR vaccine without any specific MMR allergy testing. So in reality, the relationship with egg allergy and the MMR vaccine is just in theory, as almost all egg-allergic children can receive the MMR, egg-based vaccine without a problem. However, this does not apply to other egg-based vaccines like the flu vaccine. In this case, if a child is allergic to eggs, he or she should not receive the vaccine unless specific "flu- vaccine allergy tests" are performed by an allergist. There seem to be some people that despite having an egg allergy are not allergic to the fu vaccine when tested.
Although a person can be allergic to any vaccine or any of its components or parts, this is quite rare. However there are some people that are allergic to the DT (Diphtheria, Tetanus) vaccine that is administered routinely during the first few years of life. The reason I focus on DT is that other newer vaccines, have been developed using the DT as a base; Such "DT-based vaccines" include the Meningitis vaccines. So a person, who has an allergy to DT, can theoretically be allergic to a DT based meningitis vaccine. Again, specific allergy testing for DT may be helpful.
Bottom line: if your child has an egg allergy or has had an allergic reaction to any vaccine in the past, you should discuss this with your health care professional before proceeding with any other vaccination.