Listed in Issue 240


ROULEAU and COLLEAGUES,  (1)Centre hospitalier universitaire de Québec, Quebec City, Quebec, Canada investigated the incidence of anaphylaxis following AS03-adjuvanted H1N1pdm09 vaccine.


Anaphylaxis after trivalent influenza vaccination is typically reported at a rate of <1 per million doses. In Quebec, Canada, anaphylaxis following administration of the monovalent AS03-adjuvanted H1N1pdm09 vaccine was reported through passive surveillance at a rate of 8 per million doses administered. This was 20 times higher than the reporting rate for non-adjuvanted trivalent vaccines administered during the six previous seasons. However, adequate estimation of the incidence of anaphylaxis is hindered by wide variations in definitions and diagnosis.


Using the Brighton collaboration case definition of anaphylaxis, all cases with allergic symptoms (AS) reported to public health were reviewed to estimate the incidence of anaphylaxis following AS03-adjuvanted H1N1pdm09 vaccine.


Among 752 reports of allergic symptoms, 33 were initially reported as anaphylaxis of which 20/33 (60%) met the Brighton definition (19/20 with certainty levels 1 or 2). A total of 38 additional cases with onset within 1h of vaccination also met the Brighton definition of anaphylaxis (27 (71%) with certainty levels 1 or 2). The 58 cases meeting Brighton Level 1 or 2 criteria for anaphylaxis represent a 75% increase over the 33 passively reported and an incidence of 13 per million doses administered.


A substantial number of patients with early-onset allergic symptoms met the most specific levels of the Brighton case definition but were not reported as anaphylaxis. Based on this specific case definition, the incidence of anaphylaxis after AS03-adjuvanted H1N1pdm09 vaccine substantially exceeded that reported with seasonal influenza vaccines, a signal that warrants better understanding.


Rouleau I(1), De Serres G, Drolet JP, Skowronski DM, Ouakki M, Toth E, Landry M,  Ménard S, Gagnon R. Increased risk of anaphylaxis following administration of 2009 AS03-adjuvanted monovalent pandemic A/H1N1 (H1N1pdm09) vaccine. Vaccine. 31(50):5989-96. Dec 5 2013. doi: 10.1016/j.vaccine.2013.10.033. Epub Oct 19 2013.


The data from the above research indicate that the incidence of anaphylaxis following the administration of an H1N1 vaccine exceeded reported with seasonal influenza vaccines.

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