Occurrence of vaccine strain serotype I derived polio virus in Da-hua County surrounding area, Guangxi

Objective To make case investigation for the vaccine-associated paralytic patient(VAPP) who occurred in Da-hua County,Guangxi.To carry out a series of surveillance for vaccine-derived polioviruses(VDPVs) and to estimate the poliovirus specific immunity in local children. Methods Polioviruses were isolated with RDa and L20B cells and serotypes were classified through antibodies neutralizing test(NT) before VP1 gene sequencing. The sera poliovirus Abs in local children were determined with ELISA and NT respectively. Results The type Ⅰ VDPV with 1.4% divergence in VP1 gene was identified from the 10050 case, and 6 type Ⅰ VDPVs with 1.6% ～ 2.2% divergence in VP1 gene were also isolated from 6 local healthy children during latter surveillance. The poliovirus IgG positive rate reached 77.4% , and the activity of neutralizing Abs against type Ⅱ poliovirus was higher than against type Ⅰ and type Ⅲ in local children. Conclusions This VDPV occurred in a youngster who was not immunized with OPV, and VDPVs had a short-term circulation in the local areas. The activity of type Ⅰ and type Ⅲ poliovirus neutralizing Abs was relatively lower, thereby higher OPV coverage should be maintain to prevent the potential endangerment of VDPVs.