title: Substantial decline in hepatitis B virus infections following vaccine introduction in Tajikistan.
abstract: BACKGROUND
  Tajikistan, considered highly endemic area for hepatitis B virus (HBV) in a pre-vaccine era, introduced hepatitis B vaccine in 2002 and reported ≥80% coverage with three doses of hepatitis B vaccine (HepB3) since 2004. However, the impact of vaccine introduction has not been assessed.
  
  
  METHODS
  We tested residual serum specimens from a 2010 national serosurvey for vaccine-preventable diseases in Tajikistan and assessed the prevalence of HBV infection across groups defined based on the birth cohorts' routine infant hepatitis B vaccination program implementation and HepB3 coverage achieved (≥80% versus <80%). Serosurvey participants were selected through stratified multi-stage cluster sampling among residents of all regions of Tajikistan aged 1-24 years. All specimens were tested for antibodies against HBV core antigen (anti-HBc) and those found positive were tested for HBV surface antigen (HBsAg). Seroprevalence and 95% confidence intervals were calculated and compared across subgroups using Satterthwaite-adjusted chi-square tests, accounting for the survey design and sampling weights.
  
  
  RESULTS
  A total of 2188 samples were tested. Prevalence of HBV infection markers was lowest among cohorts with ≥80% HepB3 coverage (ages, 1-6 years): 2.1% (95% confidence interval, 1.1-4.3%) for anti-HBc, 0.4% (0.1-1.3%) for HBsAg, followed by 7.2% (4.1-12.4%) for anti-HBc and 2.1% (0.7-6.1%) for HBsAg among cohorts with <80% HepB3 coverage (ages, 7-8 years), by 12.0% (8.7-16.3%) for anti-HBc and 3.5% (2.2-5.6%) for HBsAg among children's cohorts not targeted for vaccination (ages, 9-14 years), and 28.9% (24.5-33.8%) for anti-HBc and 6.8% (4.5-10.1%) for HBsAg among unvaccinated adult cohorts (ages, 15-24 years). Differences across groups were significant (p<0.001, chi-square) for both markers.
  
  
  CONCLUSIONS
  The present study demonstrates substantial impact of hepatitis B vaccine introduction on reducing HBV infections in Tajikistan. To achieve further progress in hepatitis B control, Tajikistan should maintain high routine coverage with hepatitis B vaccine, including birth dose.
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA, USA. Electronic address: nck7@cdc.gov.
authors.forename: Nino
authors.initials: N
authors.lastname: Khetsuriani
authors.affiliation: Ministry of Health of Tajikistan, Dushanbe, Tajikistan.
authors.forename: Faina
authors.initials: F
authors.lastname: Tishkova
authors.affiliation: Ministry of Health of Tajikistan, Dushanbe, Tajikistan.
authors.forename: Shamsidin
authors.initials: S
authors.lastname: Jabirov
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Wannemuehler
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Saleem
authors.initials: S
authors.lastname: Kamili
authors.affiliation: World Health Organization (WHO) Country Office, Dushanbe, Tajikistan.
authors.forename: Zulfiya
authors.initials: Z
authors.lastname: Pirova
authors.affiliation: WHO Regional Office for Europe, Copenhagen, Denmark.
authors.forename: Liudmila
authors.initials: L
authors.lastname: Mosina
authors.affiliation: WHO Regional Office for Europe, Copenhagen, Denmark.
authors.forename: Eugene
authors.initials: E
authors.lastname: Gavrilin
authors.affiliation: World Health Organization (WHO) Country Office, Dushanbe, Tajikistan.
authors.forename: Pavel
authors.initials: P
authors.lastname: Ursu
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Jan
authors.initials: J
authors.lastname: Drobeniuc
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D006509:Hepatitis B / Q000453:epidemiology* / Q000517:prevention & control*; D006510:Hepatitis B Antibodies / Q000097:blood*; D006514:Hepatitis B Surface Antigens / Q000097:blood* / Q000276:immunology; D017325:Hepatitis B Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D006801:Humans; D007223:Infant; D008297:Male; D016036:Seroepidemiologic Studies; D013620:Tajikistan / Q000453:epidemiology; D055815:Young Adult
chemical_list: D006510:Hepatitis B Antibodies; D006514:Hepatitis B Surface Antigens; D017325:Hepatitis B Vaccines
keywords: Hepatitis B immunization; Hepatitis B vaccine impact; Hepatitis B virus infections; Prevalence of HBsAg; Tajikistan; WHO European Region