title: Cross-reacting antibodies against the pandemic (H1N1) 2009 influenza virus in older Australians.
abstract: OBJECTIVE
  To assess background pre-pandemic cross-reacting antibodies to the pandemic (H1N1) 2009 virus in older populations in Australia.
  
  
  METHODS
  Data were opportunistically generated from three cross-sectional pre-pandemic studies involving people aged 60 years or older: a 3-year (2006-2008) study of influenza outbreaks in aged care facilities (ACFs) in Sydney; an investigation of a respiratory virus outbreak in an ACF in rural New South Wales in June 2009; and a non-influenza serosurvey undertaken in NSW in 2007 and 2008.
  
  
  METHODS
  Prevalence of pandemic (H1N1) 2009 haemagglutination inhibition (HAI) antibody titres ≥ 1:40 (putative protective level) in pre-pandemic sera.
  
  
  RESULTS
  In total, 259 serum samples from individuals aged 60 years or older (range, 60-101 years) were tested. More than half of the individuals tested were women (151/259; 58.3%). About a third of individuals (37.5%) had cross-reacting HAI antibody titres ≥ 1:40. The prevalence of cross-reacting antibodies was highest in the oldest age groups (≥ 85 years), with more than 60% of these people having HAI antibody titres ≥ 1:40. The proportion of subjects with HAI antibody titres ≥ 1:40 decreased significantly and successively in younger groups to only 12% of those aged 60-64 years.
  
  
  CONCLUSIONS
  Our study suggests a pre-existing influenza A antibody reserve in most of the oldest group of people that was cross-reactive to the new pandemic (H1N1) 2009 virus; this is likely to be lifelong and to have provided them with clinical protection against the first wave of the pandemic. Pandemic influenza control measures need to focus more on younger adults naive to the pandemic virus and at increased risk of severe disease.
authors: National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, The Children's Hospital at Westmead, Sydney, NSW, Australia. RobertB2@chw.edu.au
authors: Robert
authors: R
authors: Booy
authors: Gulam
authors: G
authors: Khandaker
authors: Leon G
authors: LG
authors: Heron
authors: Jiehui
authors: J
authors: Yin
authors: Bridget
authors: B
authors: Doyle
authors: Katherine K
authors: KK
authors: Tudo
authors: Linda
authors: L
authors: Hueston
authors: Gwendolyn L
authors: GL
authors: Gilbert
authors: C Raina
authors: CR
authors: Macintyre
authors: Dominic E
authors: DE
authors: Dwyer
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D003430:Cross-Sectional Studies; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009517:New South Wales / Q000453:epidemiology; D058873:Pandemics; D015995:Prevalence
chemical_list: D000914:Antibodies, Viral