title: Response to 2009 pandemic influenza A (H1N1) vaccine in HIV-infected patients and the influence of prior seasonal influenza vaccination.
abstract: BACKGROUND
  The immunogenicity of 2009 pandemic influenza A(H1N1) (pH1N1) vaccines and the effect of previous influenza vaccination is a matter of current interest and debate. We measured the immune response to pH1N1 vaccine in HIV-infected patients and in healthy controls. In addition we tested whether recent vaccination with seasonal trivalent inactivated vaccine (TIV) induced cross-reactive antibodies to pH1N1. (clinicaltrials.gov Identifier:NCT01066169).
  
  
  RESULTS
  In this single-center prospective cohort study MF59-adjuvanted pH1N1 vaccine (Focetria®, Novartis) was administered twice to 58 adult HIV-infected patients and 44 healthy controls in November 2009 (day 0 and day 21). Antibody responses were measured at baseline, day 21 and day 56 with hemagglutination-inhibition (HI) assay. The seroprotection rate (defined as HI titers ≥ 1 : 40) for HIV-infected patients was 88% after the first and 91% after the second vaccination. These rates were comparable to those in healthy controls. Post-vaccination GMT, a sensitive marker of the immune competence of a group, was lower in HIV-infected patients. We found a high seroprotection rate at baseline (31%). Seroprotective titers at baseline were much more common in those who had received 2009-2010 seasonal TIV three weeks prior to the first dose of pH1N1 vaccine. Using stored serum samples of 51 HIV-infected participants we measured the pH1N1 specific response to 2009-2010 seasonal TIV. The seroprotection rate to pH1N1 increased from 22% to 49% after vaccination with 2009-2010 seasonal TIV. Seasonal TIV induced higher levels of antibodies to pH1N1 in older than in younger subjects.
  
  
  CONCLUSIONS
  In HIV-infected patients on combination antiretroviral therapy, with a median CD4+ T-lymphocyte count above 500 cells/mm(3), one dose of MF59-adjuvanted pH1N1 vaccine induced a high seroprotection rate comparable to that in healthy controls. A second dose had a modest additional effect. Furthermore, seasonal TIV induced cross-reactive antibodies to pH1N1 and this effect was more pronounced in older subjects.
authors.affiliation: Department of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands. d.soonawala@lumc.nl
authors.forename: Darius
authors.initials: D
authors.lastname: Soonawala
authors.forename: Guus F
authors.initials: GF
authors.lastname: Rimmelzwaan
authors.forename: Luc B S
authors.initials: LB
authors.lastname: Gelinck
authors.forename: Leo G
authors.initials: LG
authors.lastname: Visser
authors.forename: Frank P
authors.initials: FP
authors.lastname: Kroon
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000097:blood; D000917:Antibody Formation; D023241:Antiretroviral Therapy, Highly Active; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D016022:Case-Control Studies; D005260:Female; D015658:HIV Infections / Q000150:complications / Q000276:immunology* / Q000628:therapy*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology* / Q000627:therapeutic use; D007251:Influenza, Human / Q000150:complications / Q000276:immunology* / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D058873:Pandemics
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines