title: Hemagglutination inhibiting antibodies and protection against seasonal and pandemic influenza infection.
abstract: OBJECTIVE
  Hemagglutination inhibiting (HI) antibodies correlate with influenza vaccine protection but their association with protection induced by natural infection has received less attention and was studied here.
  
  
  METHODS
  940 people from 270 unvaccinated households participated in active ILI surveillance spanning 3 influenza seasons. At least 494 provided paired blood samples spanning each season. Influenza infection was confirmed by RT-PCR on nose/throat swabs or serum HI assay conversion.
  
  
  RESULTS
  Pre-season homologous HI titer was associated with a significantly reduced risk of infection for H3N2 (OR 0.61, 95%CI 0.44-0.84) and B (0.65, 95%CI 0.54-0.80) strains, but not H1N1 strains, whether re-circulated (OR 0.90, 95%CI 0.71-1.15), new seasonal (OR 0.86, 95%CI 0.54-1.36) or pandemic H1N1-2009 (OR 0.77, 95%CI 0.40-1.49). The risk of seasonal and pandemic H1N1 decreased with increasing age (both p < 0.0001), and the risk of pandemic H1N1 decreased with prior seasonal H1N1 (OR 0.23, 95%CI 0.08-0.62) without inducing measurable A/California/04/2009-like titers.
  
  
  CONCLUSIONS
  While H1N1 immunity was apparent with increasing age and prior infection, the effect of pre-season HI titer was at best small, and weak for H1N1 compared to H3N2 and B. Antibodies targeting non-HI epitopes may have been more important mediators of infection-neutralizing immunity for H1N1 compared to other subtypes in this setting.
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK; The University of Melbourne, Peter Doherty Institute for Infection and Immunity, Department of Microbiology and Immunology, Parkville, Victoria, Australia. Electronic address: afox@oucru.org.
authors.forename: Annette
authors.initials: A
authors.lastname: Fox
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Le Quynh
authors.initials: le Q
authors.lastname: Mai
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Le Thi
authors.initials: le T
authors.lastname: Thanh
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Marcel
authors.initials: M
authors.lastname: Wolbers
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Nguyen
authors.initials: N
authors.lastname: Le Khanh Hang
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Pham Quang
authors.initials: PQ
authors.lastname: Thai
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Nguyen
authors.initials: N
authors.lastname: Thi Thu Yen
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam.
authors.forename: Le Nguyen
authors.initials: le N
authors.lastname: Minh Hoa
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Juliet E
authors.initials: JE
authors.lastname: Bryant
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Tran Nhu
authors.initials: TN
authors.lastname: Duong
authors.affiliation: Ha Nam Centre for Preventive Medicine, Ha Nam, Viet Nam.
authors.forename: Dang Dinh
authors.initials: DD
authors.lastname: Thoang
authors.affiliation: World Health Organization Collaborating Centre for Reference and Research on Influenza, Victorian Infectious Diseases Reference Laboratory, North Melbourne, Australia.
authors.forename: Ian G
authors.initials: IG
authors.lastname: Barr
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Heiman
authors.initials: H
authors.lastname: Wertheim
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Farrar
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Nguyen Tran
authors.initials: NT
authors.lastname: Hien
authors.affiliation: Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Viet Nam; Center for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Horby
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D057134:Antibodies, Neutralizing / Q000097:blood / Q000276:immunology*; D000914:Antibodies, Viral / Q000097:blood / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006384:Hemagglutination / Q000276:immunology*; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral
keywords: Antibody; Hemagglutination inhibition tests; Human; Humans; Humoral; Immunity; Influenza; Neutralizing; Pandemics