title: Population immunity to polioviruses in the context of a large-scale wild poliovirus type 1 outbreak in Tajikistan, 2010.
abstract: BACKGROUND
  A serosurvey to evaluate population immunity to polioviruses (PVs) in the context of the importation-related wild PV1 outbreak in Tajikistan in 2010 (461 confirmed cases among children and young adults) was conducted.
  
  
  METHODS
  Serum specimens from a nationwide sample of 1-24 year-old persons selected through stratified cluster sampling (n=2447) were tested for neutralizing antibodies to all three PV types. Samples with titers<1:8 were considered seronegative. The serosurvey was conducted during the interval after mOPV1 supplementary immunization activities (SIAs) and before tOPV SIAs (targeting ages ≤ 15 years) implemented to control the outbreak. In the absence of pre-outbreak specimens, results for PV3 were used as a proxy for pre-outbreak PV1 immunity patterns.
  
  
  RESULTS
  Overall, PV1 seroprevalence was 98.9%, PV2 seroprevalence was 98.8%, and PV3 seroprevalence was 86.9%. PV1 and PV2 seroprevalence exceeded 95% in all age groups and regions. PV3 seroprevalence was <90% in all age groups and regions, except 15-19 year-olds (91.7%) and Dushanbe (90.0%). PV3 seroprevalence was lowest among 1-4 (82.7%) and 5-9 (84.4%) year-olds, particularly among 1-4 year-olds in Kurgan-Tube (76.3%) and RRS (80.0%) regions. Birth cohorts immunized only through routine services (ages, 1-7 years) had lower PV3 seroprevalence than birth cohorts targeted by the SIAs during 1995-2002 (8-19 years): 82.5% versus 89.3%, p<0.001.
  
  
  CONCLUSIONS
  Suboptimal (<90%) PV3 seroprevalence across wide age range suggests the outbreak resulted from accumulation of susceptibles due to suboptimal coverage over a long time period, particularly in the birth cohorts immunized only through routine services and in areas where the outbreak began (Kurgan-Tube and RRS). High PV1 seroprevalence indicates that mOPV1 SIAs with expanded target age (≤ 15 years) succeeded in closing the immunity gap and ongoing WPV1 transmission is unlikely. To accelerate outbreak control in areas which have been polio-free for long time, expanding SIA target age should be considered.
authors.affiliation: Global Immunization Division, Center for Global Health, CDC, Atlanta, USA. Electronic address: nck7@cdc.gov.
authors.forename: Nino
authors.initials: N
authors.lastname: Khetsuriani
authors.forename: Mark A
authors.initials: MA
authors.lastname: Pallansch
authors.forename: Shamsiddin
authors.initials: S
authors.lastname: Jabirov
authors.forename: Nargis
authors.initials: N
authors.lastname: Saparova
authors.forename: M Steven
authors.initials: MS
authors.lastname: Oberste
authors.forename: Kathleen
authors.initials: K
authors.lastname: Wannemuehler
authors.forename: Pavel
authors.initials: P
authors.lastname: Ursu
authors.forename: Steve
authors.initials: S
authors.lastname: Wassilak
authors.forename: Rebecca
authors.initials: R
authors.lastname: Martin
mesh_terms: D000293:Adolescent; D057134:Antibodies, Neutralizing / Q000097:blood; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D011051:Poliomyelitis / Q000453:epidemiology* / Q000517:prevention & control*; D017955:Poliovirus / Q000276:immunology*; D016036:Seroepidemiologic Studies; D013620:Tajikistan / Q000453:epidemiology; D055815:Young Adult
chemical_list: D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral
keywords: Antibodies against polioviruses; Poliomyelitis; Poliomyelitis outbreaks; Polioviruses; Population immunity; Seroprevalence; Tajikistan
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