Written by Josephine Tolin
The Pakistan-Afghanistan focus of endemic poliovirus transmission is the last place in the world with ongoing evidence of still widespread infection. But the last case in this focus and in the world is anticipated to occur in 2017 or 2018. Three years after that, the plan is to eliminate all oral polio vaccine (OPV) because transmission of that live vaccine, which has been essential to achieve eradication, can evolve into as much of a problem as wild polio virus (WPV). A recent analysis, however, indicates that in places like Pakistan-Afghanistan where transmission has persisted for a long time because of difficulties achieving adequate vaccination levels, silent circulation of polioviruses could continue well beyond three years (JS Koopman et al. Dynamics affecting the risk of silent circulation when oral polio vaccination is stopped, Epidemics 2017). Vaccination of age groups up to age 39 with OPV before OPV use is stopped could help insure that OPV transmission is stopped. The last exportation of the Pakistani WPV was to Xinjiang, China. That outbreak was stopped by vaccinating everyone up to age 39. We plan to use the new methods developed by Michigan investigators, (RA Smith, EL Ionides, AA King. Infectious Disease Dynamics Inferred from Genetic Data via Sequential Monte Carlo. Molecular Biology and Evolution, April 2017) to analyze transmission dynamics in that outbreak. The results will be used to plan studies in Pakistan-Afghanistan that can insure there is no silent circulation of WPV when OPV use is stopped.