[An epidemiological study on vaccine derived polio virus circle in Zhenfeng County of Guizhou Province]

[[[ Objective: ]]] To analyze the event and cause of vaccine derived polio virus (VDPV) circle happened at Yaoshang Village, Wanlan Township, Zhenfeng County, Qianxinan Prefecture, Guizhou Province in August 2004. [[[ Methods: ]]] Virus isolation was performed for stool specimens collected from two children cases with acute flaccid paralysis (AFP) reported at Yaoshang Village and 21 normal children under five years old in the same village. And, routine immunization coverage at the Village and AFP incidence and performance of AFP surveillance system in Zhenfeng County were investigated, as well. [[[ Results: ]]] Vaccine derived polio virus 1 (VDPV1) was identified in the feces of two affected children at Yaoshang Village and three other normal children at the same village. Totally, seven cases of AFP have been underreported in Zhenfeng County since 2002. Routine immunization coverage was rather low at Wanlan Township, and nearly nil at Yaoshang Village. [[[ Conclusions: ]]] Oral polio vaccine (OPV) with attenuated live virus has been used in China for many years to prevent polio. Circulation of VDPV in Zhenfeng County issues a new challenge to eradication of polio. It is necessary to strengthen routine immunization and AFP surveillance to prevent occurrence of VDPV event.