title: Immunogenicity of a half-dose of adjuvanted 2009 pandemic H1N1 influenza vaccine in adults: a prospective cohort study.
abstract: We aimed to assess the immunogenicity of a single half-dose of AS03-adjuvanted monovalent 2009 pandemic H1N1 vaccine in healthy adults. Healthy subjects age 20-60 years were prospectively enrolled in a cohort receiving intramuscular administration of a single half-dose (1.875 μg of hemagglutinin [HA]) of adjuvanted 2009 pandemic H1N1 influenza vaccine. Data from participants enrolled in a concomitant study of immunogenicity following a full-dose (3.75 μg of HA) are presented concurrently. Sera for assessment of hemagglutination-inhibiting (HAI) antibody to the vaccine strain were obtained before and 14 or 21 days after vaccination. Ninety-seven participants received a half-dose and 50 received a full-dose of vaccine. In the half-dose cohort, Food and Drug Administration criteria for immunogenicity regarding seroprotection and seroconversion rates were met for subjects aged 20-45 years, but not for those aged 46-60 years. There was no statistically significant difference in the proportion of individuals achieving a post-vaccination HAI titre of ≥1:40, the geometric mean titres of post-vaccination antibody, or the proportion of individuals with a four-fold or greater increase in antibody levels between the two cohorts. Participants 46-60 years of age were significantly less likely to be seroprotected at day 21 than those 20-45 years old in both cohorts. Immunogenicity of a half dose of adjuvanted pH1N1 influenza vaccine was adequate in subjects aged 20-45 years. Dose reduction is a possible strategy for expanding the availability in the event of vaccine shortage in this age group.
authors.affiliation: Department of Microbiology, Mount Sinai Hospital, 600 University Ave, Room 210, Toronto, Ontario, M5G 1X5, Canada. bcoleman@mtsinai.on.ca
authors.forename: B L
authors.initials: BL
authors.lastname: Coleman
authors.forename: S P
authors.initials: SP
authors.lastname: Kuster
authors.forename: J
authors.initials: J
authors.lastname: Gubbay
authors.forename: D
authors.initials: D
authors.lastname: Scheifele
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: D
authors.initials: D
authors.lastname: Low
authors.forename: N
authors.initials: N
authors.lastname: Crowcroft
authors.forename: T
authors.initials: T
authors.lastname: Mazzulli
authors.forename: L
authors.initials: L
authors.lastname: Shi
authors.forename: S A
authors.initials: SA
authors.lastname: Halperin
authors.forename: B
authors.initials: B
authors.lastname: Law
authors.forename: A
authors.initials: A
authors.lastname: McGeer
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000328:Adult; D000367:Age Factors; D000914:Antibodies, Viral / Q000097:blood; D015331:Cohort Studies; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D007273:Injections, Intramuscular; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies
chemical_list: D000276:Adjuvants, Immunologic; D000914:Antibodies, Viral; D007252:Influenza Vaccines