Epidemiologic analysis on acute flaccid paralysis cases with isolation of poliovirus strains in Xi'an in 1995-2008

The epidemiological characters of AFP cases with poliovirus was analyzed in order to acquire more knowledge of vaccine-derived poliovirus(VDPVs) and circulating vaccine-derived poliovirus(cVDPVs)and increase the sensitivity of AFP surveillance system.XI'an AFP cases with poliovirus in 1995-2008 were analyzed.The molecular characters of vaccine-derived poliovirus were analyzed by VP1 genomic sequencing technique.13 poliovirus strains were isolated from AFP cases from 1995 to 2008.The isolated rate is 4.29%.Most of them are type II and type Ⅲ strains and AFP cases are sporadic.Number of children with full immunization is more than children with no full immunization.Most of them are under 1 year old(84.62%) and the rate of paralysis residue is 84.62%.The incidence risk rate of vaccine-associated paralytic poliomyelitis(VAPP) is 0.24/1000000.One strain has been identified as vaccine-variant poliovirus which variant rate of VP1 sequence did not reach the classified standard of VDPV.VDPV emergence and cVDPVs circulation still possibly occur in course of polio-free.It is important realistic meaning to keep high-level OPV immunization rate,high quality AFP case epidemiologic investingation and virus surveillance.