Human papillomavirus vaccine in boys: background rates of potential adverse events

To determine background rates of potential adverse events following immunisation (AEFI) before expansion of the quadrivalent human papillomavirus (4vHPV) vaccination program to adolescent boys. Design, patients and setting: Retrospective analysis of hospital discharge data obtained from the Victorian Admitted Episodes Dataset and emergency department visit data obtained from the Victorian Emergency Minimum Dataset for boys aged 12 to <16 years during the period 1 July 2004 to 30 June 2009. Main outcome measures: Numbers of and incidence rates for Guillain-Barr syndrome, anaphylaxis, seizures, syncope and other potential AEFI from 1 July 2004 to 30 June 2009, and estimated numbers of events after 4vHPV vaccination assuming no association (other than temporal) with the vaccine. Results: We estimated background rates of neurological and allergic events in adolescent boys to be 252.9 and 175.2 per 100 000 person-years, respectively. Assuming an 80 vaccination rate with three doses per person - which equates to 1 440 000 doses administered nationally per year in the first 2 years of the program - about 2.4 episodes of Guillain-Barr syndrome would be expected to occur in the 6 weeks following vaccination. Within 1 day of vaccination, about 3.9 seizures, 0.3 episodes of anaphylaxis and 6.5 acute allergy presentations would be expected. Conclusions: Routinely collected health outcome administration data can inform postlicensure safety surveillance of target conditions that might be perceived as AEFI.