In terms of MMR there are two slightly different takes on the risk of allergy with MMR (given a pre existing egg allergy)
The first school of thought is that MMR is safe for children with egg allergy:
Measles, mumps, and rubella ? Most anaphylactic reactions to MMR are due to gelatin allergy. There is no relation to egg allergy since the vaccine contains no, or a minuscule amount of, egg protein. The safety of administering MMR vaccine to people with egg allergy was demonstrated in a study of 54 children who had never been vaccinated, but had confirmed egg allergy. Skin testing was performed with the vaccine in 17 children, and 3 were positive. All the children were given the MMR vaccine as a single full dose and none had immediate or delayed adverse reactions
Ref
Sakaguchi M, Nakayama T, Inouye S (1996) Food allergy to gelatin in children with systemic immediate-type reactions, including anaphylaxis, to vaccines.
Allergy Clin Immunol. 98(6 Pt 1):1058.
Ref and abstract
James JM, Burks AW, Roberson PK, Sampson HA (1995) Safe administration of the measles vaccine to children allergic to eggs.
Engl J Med. 332(19):1262.
BACKGROUND: The safety of administering the combined measles-mumps-rubella (MMR) vaccine to patients who are allergic to eggs has been debated for decades because of concern about potential anaphylaxis, since the live attenuated virus used in the vaccine is grown in cultured chick-embryo fibroblasts.
METHODS: We recruited 54 children (mean age, 18.5 months) who had not previously been vaccinated and were allergic to eggs. The children's histories of allergy were confirmed with skin tests and double-blind, placebo-controlled food-challenge tests; some children also underwent skin testing with the MMR vaccine. We then routinely administered the vaccine to the children in one subcutaneous (0.5-ml) dose.
RESULTS: All 54 children had positive results on skin testing with egg. Allergy to eggs was confirmed in 26 of the children by convincing histories of anaphylaxis after the ingestion of eggs, in 22 children by food-challenge tests, and in 6 patients by convincing histories of recent allergic reactions occurring after the ingestion of eggs. Of the 17 children who underwent skin testingwith the MMR vaccine, 3 had positive results. All 54 children received the MMR vaccine as a single subcutaneous injection; none had an immediate or delayed adverse reaction.
CONCLUSIONS: The MMR vaccine can be safely administered in a single dose to children with allergy to eggs, even those with severe hypersensitivity.
The UK school of thought seems to err on the side of caution that a reaction could still be a possibility despite the evidence
this BMJ article reviews the literature and makes some sensible conclusions and in fact in 2008 the Royal Collage of physicians made the recommendation that MMR could be safely be given to children with a history of egg allergy in primary care, there is no need for hospital administration. There has been no major concerns raised since this change in guidelines
MMR is not the only vaccine with links to egg extract, the other vaccines that do are the flu jabs. Is this something you want more information on?
(yellow fever and rabies also do but I take it your not quite at that stage yet?
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