The human papillomavirus vaccine and risk of anaphylaxis.

509 I n this issue of CMAJ, Brotherton and colleagues 1 report a comprehensive investigation revealing higher than expected rates of apparent anaphylaxis following vaccination with the quadrivalent human papillomavirus (HPV) vaccine in Australian children. The cause of these reactions remains somewhat unclear and needs further investigation. Of note, rates of anaphylaxis, if confirmed, may not be as high in other populations. Further investigations may assist in clarifying differences between the Australian study and other reports. The use of a review panel with broad expertise in vaccines , allergy, immunology and pediatrics by Brotherton and colleagues and their use of the Brighton collaboration definition of anaphylaxis strengthen the evidence that the reactions were indeed anaphylaxis. This also strengthens their conclusions that the rate of anaphylaxis in the Australian population following HPV vaccination was higher than the rates observed following other vaccinations. Before concluding that the HPV vaccine is associated with higher rates of anaphylaxis than other vaccines everywhere, cases in other populations should be reviewed. In the United States, 15 cases of anaphylaxis or anaphlyactoid reactions following HPV vaccination were reported to the Vaccine Adverse Events Reporting System in 2007. As of July 21, 2008, 11 cases have been reported in 2008. Over 13 million doses of this vaccine had been distributed as of the end of 2007. 2 Although there may be underreporting, the rate of about one case per one million vaccinations is consistent with the rate of anaphylaxis following several other vaccines. Regardless of the true rate, the causes of rare serious adverse events should be identified and vaccines made as safe as possible to maximize benefits and maintain public confidence in vaccines and immunization programs. Differentiating hypersensitivity reactions from fainting and anxiety reactions can be difficult, especially in busy, school-based clinics. The Clinical Immunization Safety Assessment Network, sponsored by the US Centers for Disease Control and Prevention, has developed guidelines and an algorithm to assist clinicians in the assessment of suspected immediate hy-persensitivity reactions and decision-making about administering subsequent doses of vaccine. 3 Anaphylaxis that occurs within minutes of exposure is usually associated with pre-existing IgE antibodies induced by prior exposure to the allergen. Brotherton and colleagues speculate that the reactions observed could have been due to prior sensitization from yeast proteins in the hepatitis B vaccine or HPV antigens from prior infections. However, 5 of the 7 women developed anaphylaxis after the first dose of …