Hypersensitivity to Vaccine Components
Vaccine components can cause allergic reactions in some recipients. These reactions can be local or systemic and can include anaphylaxis or anaphylactic-like responses. The vaccine components responsible can include the vaccine antigen, animal proteins, antibiotics, preservatives (e.g., thimerosal), or stabilizers (e.g., gelatin). The most common animal protein allergen is egg protein in vaccines prepared by using embryonated chicken eggs (influenza and yellow fever vaccines). Generally, people who can eat eggs or egg products safely may receive these vaccines, while people with histories of anaphylactic allergy (e.g., hives, swelling of the mouth and throat, difficulty breathing, hypotension, or shock) to eggs or egg proteins ordinarily should not. Screening people by asking whether they can eat eggs without adverse effects is a reasonable way to identify those who might be at risk from receiving yellow fever and influenza vaccines. Recent studies have indicated that other components in vaccines in addition to egg proteins (e.g., gelatin) may cause allergic reactions, including anaphylaxis in rare instances. Protocols have been developed for testing and vaccinating people with anaphylactic reactions to egg ingestion.
Some vaccines contain preservatives or trace amounts of antibiotics to which people might be allergic. Those administering the vaccine(s) should carefully review the information provided in the package insert before deciding if the rare person with such an allergy should receive the vaccine(s). Thimerosal in trace quantities may be found in the meningococcal polysaccharide vaccine (groups A, C, Y, and W-125 combined) and the Japanese encephalitis vaccines, as well as in a few others. For a listing of preservatives used and the vaccines in which they are found, see www.fda.gov/cber/vaccine/thimerosal.htm. No currently recommended vaccine contains penicillin or penicillin derivatives. Some vaccines (e.g., MMR and its individual component vaccines, IPV, varicella, rabies) contain trace amounts of neomycin or other antibiotics; the amount is less than would normally be used for the skin test to determine hypersensitivity. However, people who have experienced anaphylactic reactions to the antibiotic generally should not receive these vaccines. Most often, neomycin allergy is a contact dermatitis—a manifestation of a delayed-type (cell-mediated) immune response—rather than anaphylaxis. A history of delayed-type reactions to neomycin is not a contraindication to receiving these vaccines.
