| evolution and circulation of type-2 vaccine-derived polioviruses in nad ali district of southern afghanistan during june 2009-february 2011. | oral polio vaccine has been used successfully as a powerful tool to control the spread of wild polioviruses throughout the world; however, during replication in under immunized children, some vaccine viruses revert and acquire the neurovirulent phenotypic properties. in this study, we describe the evolution and circulation of vaccine-derived polioviruses (vdpvs) in helmand province of afghanistan. we investigated 2646 afp cases of afghan children from june 2009-february 2011 and isolated 103 (04 ... | 2014 | 24558390 |