Population immunity to polioviruses in the context of a large-scale wild poliovirus type 1 outbreak in Tajikistan, 2010

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.