VAPP mostly occurred in children< 1 year old after one dose of OPV vaccine.

主要发生在< 1岁儿童，且多为首次服苗后。

The OPV also reports that 221 prisoners were murdered in the first six months of this year alone.

OPV还称，仅今年的前六个月，就有221名囚犯被谋杀。

In this thesis, some basic research work is carried out based on OEL and OPV characteristics.

本论文基于此开展了一些探讨性的研究工作。

A: a vaccine-derived poliovirus (VDPV) is a rare strain of poliovirus, genetically mutated from the strain contained in oral polio vaccine (OPV).

答：疫苗衍生脊髓灰质炎病毒(VDPV)是一种罕见的脊髓灰质炎病毒株，由口服脊髓灰质炎疫苗(opv)里的病毒株遗传变异而来。

Henceforth it is advisable to enhance the training force of clinicians at county-level medical facilities to further improve OPV immunization rate.

今后应加大对县级医疗机构临床医生的培训力度，进一步提高OPV免疫接种率。