10/20/03 Allergic reactions to vaccinesSummaryImmunization programs have been one of the most successful medical/public health measures with a very low incidence of truly allergic reactions to the standard vaccines in use. Kelso of the National Naval Medical Center in San Diego, CA reviewed the nature of the very occasional allergic reactions to vaccine. He pointed out that true allergic reactions occur within 4 hours after the vaccine injection and are usually manifest by the skin, respiratory and occasionally cardiovascular manifestations seen in anaphylactic reactions to other medications. The allergic reactions are usually directed against non-microbial components of the vaccine, such as egg protein (in egg sensitive subjects) or gelatin. The amount of egg protein (from chicken embryos) present in the MMR and usual rabies vaccines is so small that these vaccines do not present an increased risk in egg-sensitive individuals. A much higher concentration of egg protein is present in influenza and yellow fever vaccines. Thus, individual with histories of egg allergy should be tested for current egg allergy in advance. If the individual is reactive to egg and the vaccine is definitely needed, a graded dose injection program is advisable. Gelatin is present as a stabilizer in a number of vaccines with the highest concentrations in MMR, rabies, varicella and yellow fever vaccines. Anaphylactic reactions have been reported as a very infrequent adverse reaction to such vaccines. Gelatin-free vaccines are in development but the current approach is to inject graded doses under close observation for several hours afterwards. Allergic reactions to neomycin or thiomersal present in some vaccines are rare events. Thiomersal-free vaccines are now becoming available for pediatric immunization programs because of concerns about possible CNS adverse effects of the cumulative exposure to mercury (in the thiomersal) in young children. Reference J Respir Dis 2003;24:409-16 Editor's Comments This discussion by a very experienced investigator of vaccine-induced allergic reactions puts such reactions into a sound perspective with helpful suggestions about the approaches involved. It is worth reading and keeping on file.
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