title: Detection of extensive cross-neutralization between pandemic and seasonal A/H1N1 Influenza Viruses using a pseudotype neutralization assay.
abstract: BACKGROUND
  Cross-immunity between seasonal and pandemic A/H1N1 influenza viruses remains uncertain. In particular, the extent that previous infection or vaccination by seasonal A/H1N1 viruses can elicit protective immunity against pandemic A/H1N1 is unclear.
  
  
  RESULTS
  Neutralizing titers against seasonal A/H1N1 (A/Brisbane/59/2007) and against pandemic A/H1N1 (A/California/04/2009) were measured using an HIV-1-based pseudovirus neutralization assay. Using this highly sensitive assay, we found that a large fraction of subjects who had never been exposed to pandemic A/H1N1 express high levels of pandemic A/H1N1 neutralizing titers. A significant correlation was seen between neutralization of pandemic A/H1N1 and neutralization of a standard seasonal A/H1N1 strain. Significantly higher pandemic A/H1N1 neutralizing titers were measured in subjects who had received vaccination against seasonal influenza in 2008-2009. Higher pandemic neutralizing titers were also measured in subjects over 60 years of age.
  
  
  CONCLUSIONS
  Our findings reveal that the extent of protective cross-immunity between seasonal and pandemic A/H1N1 influenza viruses may be more important than previously estimated. This cross-immunity could provide a possible explanation of the relatively mild profile of the recent influenza pandemic.
authors.affiliation: Institut Universitaire d'Hématologie, Université Paris Diderot, Paris, France.
authors.forename: Béatrice
authors.initials: B
authors.lastname: Labrosse
authors.forename: Mathieu
authors.initials: M
authors.lastname: Tourdjman
authors.forename: Raphaël
authors.initials: R
authors.lastname: Porcher
authors.forename: Jérôme
authors.initials: J
authors.lastname: LeGoff
authors.forename: Xavier
authors.initials: X
authors.lastname: de Lamballerie
authors.forename: François
authors.initials: F
authors.lastname: Simon
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Molina
authors.forename: François
authors.initials: F
authors.lastname: Clavel
mesh_terms: D015497:HIV-1 / Q000276:immunology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D008875:Middle Aged; D009500:Neutralization Tests; D012680:Sensitivity and Specificity