title: Post-pandemic seroprevalence of pandemic influenza A (H1N1) 2009 infection (swine flu) among children <18 years in Germany.
abstract: BACKGROUND
  We determined antibodies to the pandemic influenza A (H1N1) 2009 virus in children to assess: the incidence of (H1N1) 2009 infections in the 2009/2010 season in Germany, the proportion of subclinical infections and to compare titers in vaccinated and infected children.
  
  
  RESULTS
  Eight pediatric hospitals distributed over Germany prospectively provided sera from in- or outpatients aged 1 to 17 years from April 1(st) to July 31(st) 2010. Vaccination history, recall of infections and sociodemographic factors were ascertained. Antibody titers were measured with a sensitive and specific in-house hemagglutination inhibition test (HIT) and compared to age-matched sera collected during 6 months before the onset of the pandemic in Germany. We analyzed 1420 post-pandemic and 300 pre-pandemic sera. Among unvaccinated children aged 1-4 and 5-17 years the prevalence of HI titers (≥1∶10) was 27.1% (95% CI: 23.5-31.3) and 53.5% (95% CI: 50.9-56.2) compared to 1.7% and 5.5%, respectively, for pre-pandemic sera, accounting for a serologically determined incidence of influenza A (H1N1) 2009 during the season 2009/2010 of 25,4% (95% CI : 19.3-30.5) in children aged 1-4 years and 48.0% (95% CI: 42.6-52.0) in 5-17 year old children. Of children with HI titers ≥1∶10, 25.5% (95% CI: 22.5-28.8) reported no history of any infectious disease since June 2009. Among vaccinated children, 92% (95%-CI: 87.0-96.6) of the 5-17 year old but only 47.8% (95%-CI: 33.5-66.5) of the 1-4 year old children exhibited HI titers against influenza A virus (H1N1) 2009.
  
  
  CONCLUSIONS
  Serologically determined incidence of influenza A (H1N1) 2009 infections in children indicates high infection rates with older children (5-17 years) infected twice as often as younger children. In about a quarter of the children with HI titers after the season 2009/2010 subclinical infections must be assumed. Low HI titers in young children after vaccination with the AS03(B)-adjuvanted split virion vaccine need further scrutiny.
authors.affiliation: Institut für Soziale Pädiatrie und Jugendmedizin, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: von Kries
authors.forename: Susanne
authors.initials: S
authors.lastname: Weiss
authors.forename: Gerhard
authors.initials: G
authors.lastname: Falkenhorst
authors.forename: Stephan
authors.initials: S
authors.lastname: Wirth
authors.forename: Petra
authors.initials: P
authors.lastname: Kaiser
authors.forename: Hans-Iko
authors.initials: HI
authors.lastname: Huppertz
authors.forename: Tobias
authors.initials: T
authors.lastname: Tenenbaum
authors.forename: Horst
authors.initials: H
authors.lastname: Schroten
authors.forename: Andrea
authors.initials: A
authors.lastname: Streng
authors.forename: Johannes
authors.initials: J
authors.lastname: Liese
authors.forename: Sonu
authors.initials: S
authors.lastname: Shai
authors.forename: Tim
authors.initials: T
authors.lastname: Niehues
authors.forename: Hermann
authors.initials: H
authors.lastname: Girschick
authors.forename: Ellen
authors.initials: E
authors.lastname: Kuscher
authors.forename: Axel
authors.initials: A
authors.lastname: Sauerbrey
authors.forename: Jochen
authors.initials: J
authors.lastname: Peters
authors.forename: Carl Heinz
authors.initials: CH
authors.lastname: Wirsing von König
authors.forename: Simon
authors.initials: S
authors.lastname: Rückinger
authors.forename: Walter
authors.initials: W
authors.lastname: Hampl
authors.forename: Detlef
authors.initials: D
authors.lastname: Michel
authors.forename: Thomas
authors.initials: T
authors.lastname: Mertens
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D002648:Child; D002675:Child, Preschool; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000472:pathogenicity*; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D016036:Seroepidemiologic Studies
chemical_list: D007252:Influenza Vaccines