title: Response to a monovalent 2009 influenza A (H1N1) vaccine.
abstract: BACKGROUND
  A novel 2009 influenza A (H1N1) virus is responsible for the first influenza pandemic in 41 years. A safe and effective vaccine is needed. A randomized, observer-blind, parallel-group trial evaluating two doses of an inactivated, split-virus 2009 H1N1 vaccine in healthy adults between the ages of 18 and 64 years is ongoing at a single site in Australia.
  
  
  METHODS
  We evaluated the immunogenicity and safety of the vaccine after each of two scheduled doses, administered 21 days apart. A total of 240 subjects, equally divided into two age groups (<50 years and >or=50 years), were enrolled and underwent randomization to receive either 15 microg or 30 microg of hemagglutinin antigen by intramuscular injection. We measured antibody titers using hemagglutination-inhibition and microneutralization assays at baseline and 21 days after vaccination. The coprimary immunogenicity end points were the proportion of subjects with antibody titers of 1:40 or more on hemagglutination-inhibition assay, the proportion of subjects with either seroconversion or a significant increase in antibody titer, and the factor increase in the geometric mean titer.
  
  
  RESULTS
  By day 21 after the first dose, antibody titers of 1:40 or more were observed in 114 of 120 subjects (95.0%) who received the 15-microg dose and in 106 of 119 subjects (89.1%) who received the 30-microg dose. A similar result was observed after the second dose of vaccine. No deaths, serious adverse events, or adverse events of special interest were reported. Local discomfort (e.g., injection-site tenderness or pain) was reported by 56.3% of subjects, and systemic symptoms (e.g., headache) by 53.8% of subjects after each dose. Nearly all events were mild to moderate in intensity.
  
  
  CONCLUSIONS
  A single 15-microg dose of 2009 H1N1 vaccine was immunogenic in adults, with mild-to-moderate vaccine-associated reactions. (ClinicalTrials.gov number, NCT00938639).
authors.affiliation: Clinical Research and Development, CSL, Parkville, VIC, Australia. michael.greenberg@csl.com.au
authors.forename: Michael E
authors.initials: ME
authors.lastname: Greenberg
authors.forename: Michael H
authors.initials: MH
authors.lastname: Lai
authors.forename: Gunter F
authors.initials: GF
authors.lastname: Hartel
authors.forename: Christine H
authors.initials: CH
authors.lastname: Wichems
authors.forename: Charmaine
authors.initials: C
authors.lastname: Gittleson
authors.forename: Jillian
authors.initials: J
authors.lastname: Bennet
authors.forename: Gail
authors.initials: G
authors.lastname: Dawson
authors.forename: Wilson
authors.initials: W
authors.lastname: Hu
authors.forename: Connie
authors.initials: C
authors.lastname: Leggio
authors.forename: Diane
authors.initials: D
authors.lastname: Washington
authors.forename: Russell L
authors.initials: RL
authors.lastname: Basser
mesh_terms: D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests; D011446:Prospective Studies; D016037:Single-Blind Method; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines