Analysis on the Occurrence of Anaphylaxis Following Influenza A H_1N_1 Vaccine Immunization in China

Objective To analyze the occurrence of anaphylaxis following Influenza A(H1N1)vaccine immunization in China during 2009-2010, and to evaluate the risk of anaphylaxis following immunization and the response to anaphylaxis. Methods Data on anaphylaxis following Influenza A(H1N1)vaccine immunization were collected through China AEFI information system by November 20, 2010. The number of doses administered was collected by reports from all provinces. The descriptive methodology was used in the study. Results 100.01 million doses were administered between September 21, 2009 and November 20, 2010, and 50 anaphylaxis cases(rate: 0.50 per million doses)were reported, with a hospitalization rate of 48.00%. The age-specific rates of anaphylaxis varied from each other, and the highest was 0.86 per million among persons aged from 20 to 59 years. The incidence rates of anaphylaxis among medical staff was 2.87 per million. The median interval from vaccination to onset was 10 minutes (range, 2-120 minutes). Conclusions This study suggested that anaphylaxis was associated with influenza A(H1N1)vaccination, but the incidence was very low, which was under the baseline, and there was no evidence for an increase risk of anaphylaxis.