title: A(H1N1)pdm09 vaccination of health care workers: improved immune responses in low responders following revaccination.
abstract: BACKGROUND
  We conducted a clinical trial in October 2009 to evaluate the immunogenicity of the AS03-adjuvanted influenza vaccine (pH1N1 vaccine) in health care workers (HCWs). By 2 weeks after vaccination, 97% had protective hemagglutinin inhibition (HI) titers (≥ 40) however, 16% were low responders (LR) and failed to maintain a protective response 90 days after vaccination.
  
  
  METHODS
  We analyzed the humoral responses (HI, antibody-secreting cell [ASC], and serum immunoglobulin G [IgG]) in 15 LRs and 25 control HCWs. Twelve LRs were revaccinated with the pH1N1 vaccine, and 7 were subsequently vaccinated with the 2010 seasonal trivalent influenza vaccine. We conducted a long-term analysis of the humoral and CD4(+) T-helper (Th) 1 responses.
  
  
  RESULTS
  The LRs had a slower HI antibody response than the control HCWs, with protective antibody titers not reached until 2 weeks after vaccination in the majority of the participants. The LRs also had significantly lower IgG ASCs at day 7 and HA1-specific serum IgG responses at day 21, compared with the control HCWs. Revaccination with the pH1N1 vaccine elicited rapid HI antibody, ASC, memory B cell, and multifunctional CD4(+) Th1 cell responses.
  
  
  CONCLUSIONS
  This study shows that revaccination of low-responding HCWs with the pH1N1 vaccine is required for maintaining long-term protection.
  
  
  BACKGROUND
  NCT01003288.
authors.affiliation: Influenza Centre, The Gade Institute, University of Bergen, Bergen, Norway. rebecca.cox@gades.uib.no
authors.forename: Rishi Delan
authors.initials: RD
authors.lastname: Pathirana
authors.forename: Geir
authors.initials: G
authors.lastname: Bredholt
authors.forename: Per Espen
authors.initials: PE
authors.lastname: Akselsen
authors.forename: Gabriel Kristian
authors.initials: GK
authors.lastname: Pedersen
authors.forename: Rebecca Jane
authors.initials: RJ
authors.lastname: Cox
mesh_terms: D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D056724:Immunity, Humoral; D007117:Immunization, Secondary; D007074:Immunoglobulin G / Q000097:blood; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*
chemical_list: D000914:Antibodies, Viral; D016207:Cytokines; D007074:Immunoglobulin G; D007252:Influenza Vaccines