title: Estimation of the herd protection of Haemophilus influenzae type b conjugate vaccine against radiologically confirmed pneumonia in children under 2 years old in Dhaka, Bangladesh.
abstract: BACKGROUND
  Herd protection of Haemophilus influenzae type b (Hib) conjugate vaccine has been associated with excessive decrease of invasive Hib diseases, i.e., pneumonia and meningitis, with increased national or regional Hib vaccine coverage. Only a few studies have examined herd protection at the individual level and even less evidence is available from Asia. We examined Hib vaccine herd protection against radiologically confirmed pneumonia among children less than 2 years old.
  
  
  METHODS
  We incorporated data from a matched case-control study and a vaccine coverage survey in Dhaka, Bangladesh. Pneumonia cases (n=343) were confirmed by radiology. For each case, two controls with conditions other than pneumonia or meningitis were selected from the same hospital. Hib vaccine coverage was calculated as percentages of children who received at least 2 doses of Hib vaccine from a survey in the neighborhood centered on each case and control. Conditional logistic regression was fit to examine the association between vaccine coverage and risk of radiologically confirmed pneumonia.
  
  
  RESULTS
  Neighborhood Hib vaccine coverage varied from 0% to 63.5% for cases and from 8.7% to 61.5% for controls, respectively. Cases were less likely to have neighborhood coverage higher than 20% (OR=0.49, 0.52, 0.55, and 0.69 for coverage 20-29%, 30-39%, 40-49%, and ≥50%, respectively) than coverage <20%, compared to controls, although the estimates for coverage 40-49% and ≥50% were not statistically significant.
  
  
  CONCLUSIONS
  The study indicates that Hib vaccine may provide herd protection, even when the coverage is as low as 20-39%, in a low-income country. Asian countries should consider herd protection in implementing effective vaccine policy with limited resources.
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, 615N. Wolfe St., Baltimore, MD 21201, USA. Electronic address: wjchen@jhsph.edu.
authors.forename: Wei-Ju
authors.initials: WJ
authors.lastname: Chen
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, 615N. Wolfe St., Baltimore, MD 21201, USA.
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Moulton
authors.affiliation: Dhaka Shishu Hospital, Syed Mahbub Morshed Ave, Shamoli, Dhaka, Bangladesh.
authors.forename: Samir K
authors.initials: SK
authors.lastname: Saha
authors.affiliation: Child Health Program, International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), 68 Shaheed Tajuddin Ahmed Sharani, Mohakhali, Dhaka, Bangladesh.
authors.forename: Abdullah Al
authors.initials: AA
authors.lastname: Mahmud
authors.affiliation: Child Health Program, International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), 68 Shaheed Tajuddin Ahmed Sharani, Mohakhali, Dhaka, Bangladesh.
authors.forename: Shams El
authors.initials: SE
authors.lastname: Arifeen
authors.affiliation: Department of International Health, Johns Hopkins Bloomberg School of Public Health, 615N. Wolfe St., Baltimore, MD 21201, USA.
authors.forename: Abdullah H
authors.initials: AH
authors.lastname: Baqui
mesh_terms: D016667:Bacterial Capsules; D001459:Bangladesh; D016022:Case-Control Studies; D005260:Female; D006192:Haemophilus Infections / Q000517:prevention & control*; D018073:Haemophilus Vaccines / Q000627:therapeutic use*; D019741:Haemophilus influenzae type b; D006801:Humans; D032521:Immunity, Herd; D007223:Infant; D008297:Male; D018410:Pneumonia, Bacterial / Q000000981:diagnostic imaging* / Q000517:prevention & control; D011859:Radiography; D014611:Vaccination / Q000706:statistics & numerical data*; D018074:Vaccines, Conjugate / Q000627:therapeutic use
chemical_list: D018073:Haemophilus Vaccines; C044237:Haemophilus influenzae type b polysaccharide vaccine; D018074:Vaccines, Conjugate
keywords: Haemophilus influenzae type b (Hib) vaccine; Herd protection; Vaccine coverage