title: Early indication for a reduced burden of radiologically confirmed pneumonia in children following the introduction of routine vaccination against Haemophilus influenzae type b in Nha Trang, Vietnam.
abstract: BACKGROUND
  Despite the global success of Hib vaccination in reducing disease and mortality, uncertainty about the disease burden and the potential impact of Hib vaccination in Southeast Asia has delayed the introduction of vaccination in some countries in the region. Hib vaccination was introduced throughout Vietnam in July 2010 without catch-up. In an observational, population based surveillance study we estimated the impact of routine Hib vaccination on all cause radiologically confirmed childhood pneumonia in Nha Trang, Vietnam.
  
  
  METHODS
  In 2007 active hospital based surveillance was established in Khanh Hoa General Hospital, the only hospital in Nha Trang, Khanh Hoa province. Nasopharyngeal samples and chest radiographs are taken routinely from all children diagnosed with acute respiratory illness on admission. For admissions between 02/2007 and 03/2012 chest radiographs were interpreted for the presence of WHO primary endpoint pneumonia and nasopharyngeal swabs were analysed by PCR for the presence of Influenza A or B, RSV and rhinovirus. We employed Poisson regression to estimate the impact of Hib vaccination on radiologically confirmed pneumonia (RCP) while statistically accounting for potential differences in viral circulation in the post vaccination era which could have biased the estimate.
  
  
  RESULTS
  Of 3151 cases admitted during the study period, 166 had RCP and major viruses were detected in 1601. The adjusted annual incidence of RCP in children younger than 5 years declined by 39% (12-58%) after introduction of Hib vaccination. This decline was most pronounced in children less than 2 years old, adjusted IRR: 0.52 (0.33-0.81), and no significant impact was observed in the 2-4 years old who were not eligible for vaccination, adjusted IRR: 0.96 (0.52-1.72).
  
  
  CONCLUSIONS
  We present early evidence that the burden of Hib associated RCP in Nha Trang before vaccination was substantial and that shortly after introduction to the routine childhood immunisation scheme vaccination has substantially reduced that burden.
authors.affiliation: London School of Hygiene and Tropical Medicine, London, UK. Electronic address: Stefan.Flasche@lshtm.ac.uk.
authors.forename: Stefan
authors.initials: S
authors.lastname: Flasche
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Dinh Thiem
authors.initials: DT
authors.lastname: Vu
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Motoi
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Thi Hien-Anh
authors.initials: TH
authors.lastname: Nguyen
authors.affiliation: Khanh Hoa Health Service Department, Nha Trang, Viet Nam.
authors.forename: HuuTho
authors.initials: H
authors.lastname: Le
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hashizume
authors.affiliation: National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam.
authors.forename: Duc Anh
authors.initials: DA
authors.lastname: Dang
authors.affiliation: Menzies School of Health Research, Darwin, Australia.
authors.forename: Karen
authors.initials: K
authors.lastname: Edmond
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Koya
authors.initials: K
authors.lastname: Ariyoshi
authors.affiliation: London School of Hygiene and Tropical Medicine, London, UK; Menzies School of Health Research, Darwin, Australia.
authors.forename: E Kim
authors.initials: EK
authors.lastname: Mulholland
authors.affiliation: London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: W John
authors.initials: WJ
authors.lastname: Edmunds
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Lay-Myint
authors.initials: LM
authors.lastname: Yoshida
mesh_terms: D002675:Child, Preschool; D062665:Epidemiological Monitoring; D005260:Female; D006192:Haemophilus Infections / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control*; D018073:Haemophilus Vaccines / Q000008:administration & dosage* / Q000276:immunology; D019741:Haemophilus influenzae type b / Q000276:immunology*; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000821:virology; D011014:Pneumonia / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control* / Q000821:virology; D015995:Prevalence; D013902:Radiography, Thoracic; D014611:Vaccination / Q000706:statistics & numerical data*; D014744:Vietnam / Q000453:epidemiology
chemical_list: D018073:Haemophilus Vaccines
keywords: Hib; Immunisation; Southeast Asia