Since MMR vaccine is prepared in chick embryo cell culture, there has been some concern in the past that it posed a  risk to children with egg allergy, particularly for those with anaphylaxis to egg.

In the past the Red Book recommended skin testing such children to MMR vaccine and administering gradually increasing doses of vaccine if the skin tests were positive.

Subsequent studies have shown that the one dose administration of MMR vaccine to egg-allergic patients is quite safe,  even in patients with a history of anaphylaxis to egg.

Studies have also shown that patients with a positive skin test to MMR vaccine can safely receive a normal dose of  MMR vaccine.

Anaphylactic reactions have occasionally been reported after MMR vaccination in patients without egg allergy, suggesting that reactions may occur to other components besides egg protein. Neomycin and gelatin have been suspected in some of these reactions.

The American Academy of Pediatrics (AAP) has revised its recommendations that MMR vaccine be given in one dose to all patients with egg allergy. However, the AAP recommends that patients be closely observed for at least 90 minutes after the injection in an office or clinic setting equipped to treat allergic reactions.