Conducting public health surveillance in areas of armed conflict and restricted population access: a qualitative case study of polio surveillance in conflict-affected areas of Borno State, Nigeria

在武装冲突和人口流动受限地区开展公共卫生监测：以尼日利亚博尔诺州受冲突影响地区脊髓灰质炎监测为例的定性案例研究