Allergic Reactions

In addition to the desired antigen, live attenuated and inactivated vaccines almost always contain other components such as residual animal or human proteins, antibacterial agents, and preservatives or stabilizers, which may cause allergic reactions. The most common allergenic component of vaccines is egg protein found in vaccines prepared in chicken eggs or chicken embryonic cultures, e.g., measles, mumps, and influenza.

Egg allergy is very common, affecting 1 to 2 percent of children.^14,15 However, with the exception of those with a high titer of egg IgE antibodies, most children are likely to develop egg tolerance by late childhood.¹⁶ Adults who can eat eggs or egg-containing products can receive these vaccines safely. On rare occasions, patients will have an anaphylactic reaction to baker's yeast found in HBV vaccines and to neomycin found in trace amounts in the measles, mumps, rubella, and varicella vaccines.