title: Immediate hypersensitivity reactions following monovalent 2009 pandemic influenza A (H1N1) vaccines: reports to VAERS.
abstract: BACKGROUND
  Hypersensitivity disorders following vaccinations are a cause for concern.
  
  
  OBJECTIVE
  To determine the type and rate by age, gender, and vaccine received for reported hypersensitivity reactions following monovalent 2009 pandemic influenza A (H1N1) vaccines.
  
  
  METHODS
  A systematic review of reports to the Vaccine Adverse Event Reporting System (VAERS) following monovalent 2009 pandemic influenza A (H1N1) vaccines.
  
  
  METHODS
  US Civilian reports following vaccine received from October 1, 2009 through May 31, 2010.
  
  
  METHODS
  Age, gender, vaccines received, diagnoses, clinical signs, and treatment were reviewed by nurses and physicians with expertise in vaccine adverse events. A panel of experts, including seven allergists reviewed complex illnesses and those with conflicting evidence for classification of the event.
  
  
  RESULTS
  Of 1984 reports, 1286 were consistent with immediate hypersensitivity disorders and 698 were attributed to anxiety reactions, syncope, or other illnesses. The female-to-male ratio was ≥4:1 for persons 20-to-59 years of age, but approximately equal for children under 10. One hundred eleven reports met Brighton Collaboration criteria for anaphylaxis; only one-half received epinephrine for initial therapy. The overall rate of reported hypersensitivity reactions was 10.7 per million vaccine doses distributed, with a 2-fold higher rate for live vaccine.
  
  
  CONCLUSIONS
  Underreporting, especially of mild events, would result in an underestimate of the true rate of immediate hypersensitivity reactions. Selective reporting of events in adult females could have resulted in higher rates than reported for males.
  
  
  CONCLUSIONS
  Adult females may be at higher risk of hypersensitivity reactions after influenza vaccination than men. Although the risk of hypersensitivity reactions following 2009 pandemic influenza A (H1N1) vaccines was low, all clinics administering vaccines should be familiar with treatment guidelines for these adverse events, including the use of intramuscular epinephrine early in the course of serious hypersensitivity reactions.
authors.affiliation: Institute for Vaccine Safety, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA. Electronic address: nhalsey@jhsph.edu.
authors.forename: Neal A
authors.initials: NA
authors.lastname: Halsey
authors.forename: Mari
authors.initials: M
authors.lastname: Griffioen
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Dreskin
authors.forename: Cornelia L
authors.initials: CL
authors.lastname: Dekker
authors.forename: Robert
authors.initials: R
authors.lastname: Wood
authors.forename: Devindra
authors.initials: D
authors.lastname: Sharma
authors.forename: James F
authors.initials: JF
authors.lastname: Jones
authors.forename: Philip S
authors.initials: PS
authors.lastname: LaRussa
authors.forename: Jenny
authors.initials: J
authors.lastname: Garner
authors.forename: Melvin
authors.initials: M
authors.lastname: Berger
authors.forename: Tina
authors.initials: T
authors.lastname: Proveaux
authors.forename: Claudia
authors.initials: C
authors.lastname: Vellozzi
authors.forename: Karen
authors.initials: K
authors.lastname: Broder
authors.forename: Rosanna
authors.initials: R
authors.lastname: Setse
authors.forename: Barbara
authors.initials: B
authors.lastname: Pahud
authors.forename: David
authors.initials: D
authors.lastname: Hrncir
authors.forename: Howard
authors.initials: H
authors.lastname: Choi
authors.forename: Robert
authors.initials: R
authors.lastname: Sparks
authors.forename: Sarah Elizabeth
authors.initials: SE
authors.lastname: Williams
authors.forename: Renata J
authors.initials: RJ
authors.lastname: Engler
authors.forename: Jane
authors.initials: J
authors.lastname: Gidudu
authors.forename: Roger
authors.initials: R
authors.lastname: Baxter
authors.forename: Nicola
authors.initials: N
authors.lastname: Klein
authors.forename: Kathryn
authors.initials: K
authors.lastname: Edwards
authors.forename: Maria
authors.initials: M
authors.lastname: Cano
authors.forename: John M
authors.initials: JM
authors.lastname: Kelso
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D064420:Drug-Related Side Effects and Adverse Reactions / Q000453:epidemiology* / Q000473:pathology; D005260:Female; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000139:chemically induced*; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000009:adverse effects*; D007251:Influenza, Human / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Allergic reactions; Anaphylaxis; H1N1 influenza vaccine; Hypersensitivity; Immunization; Influenza vaccine; Urticaria