Although the measles vaccine is produced in a chick embryo cell culture, it does not contain large amounts of egg proteins--things he could react or be allergic to. In fact, children with egg allergies are at low risk for severe allergic reactions (anaphylaxis) to the measles-containing vaccines. Persons with allergies to chicken or feathers are also not at increased risk of reaction to the vaccine. Unfortunately, allergy skin testing of children possibly allergic to eggs is not even predictive of reactions to the MMR vaccine. Thus, some experts do not even feel that there is a reason to be tested and that these children should just be vaccinated in the usual manner.
In contrast, those children who have had a past allergic (hypersensitivity) reaction to a measles vaccine can be skin tested before the second dose or their antibodies can be tested to determine if there is even a need for a second dose. Certainly, if someone has had any severe allergic reaction (anaphylaxis) to prior vaccination, they should be vaccinated only in settings where an immediate, life-threatening reaction can be managed. The bottom line is I would not want to leave him unprotected, so please continue the in depth dialogue with his doctor.