Risk of Anaphylaxis After Vaccination of Children and Adolescents

Objective. To quantify the risk of ana- phylaxis after vaccination of children and adolescents. Methods. The study population consisted of children and adolescents who were enrolled at 4 health mainte- nance organizations that participated in the Vaccine Safety Datalink Project. For the period 1991-1997, we identified potential cases by searching for occurrences of International Classification of Diseases, Ninth Revision (ICD-9) code 995.0 (anaphylactic shock), E948.0 through E948.9 (adverse reaction from bacterial vaccines), and E949.0 through E949.9 (adverse reaction from other vac- cines and biological substances). At 1 study site, we also included a range of other allergy codes. We restricted to diagnoses on days 0 to 2 after vaccination (ICD-9 995.0) or day 0 (all other ICD-9 codes). We then reviewed the medical record to confirm the diagnosis. Results. We identified 5 cases of potentially vaccine- associated anaphylaxis after administration of 7 644 049 vaccine doses, for a risk of 0.65 cases/million doses (95% confidence interval: 0.21-1.53). None of the episodes re- sulted in death. Vaccines that were administered before the anaphylactic episodes were generally given in com- bination and included measles-mumps-rubella, hepatitis B, diphtheria-tetanus, diphtheria-tetanus-pertussis, Hae- mophilus influenzae type b, and oral polio vaccine. One case of anaphylaxis followed measles-mumps-rubella vaccine alone. At the site at which we reviewed addi- tional allergy codes, we identified 1 case after 653 990 vaccine doses, for a risk of 1.53 cases/million doses (95% confidence interval: 0.04 - 8.52). Conclusions. Patients and health care providers can be reassured that vaccine-associated anaphylaxis is a rare event. Nevertheless, providers should be prepared to provide immediate medical treatment should it occur. Pediatrics 2003;112:815- 820; anaphylaxis, vaccination, vaccine adverse reactions. ABBREVIATIONS. MMR, measles-mumps-rubella; HMO, health maintenance organization; VSD, Vaccine Safety Datalink; ICD-9, International Classification of Diseases, Ninth Revision; CI, confidence interval; DT, pediatric diphtheria-tetanus; DTP, diphtheria-teta- nus-whole cell pertussis; Hib, Haemophilus influenzae type b; OPV, oral polio vaccine; VAERS, Vaccine Adverse Event Reporting System.