"The migrant worker phenomenon has led to separation of families in other countries, most notably the Philippines, but that's on a much smaller scale, and mostly cross-border," he says.

Large-scale emergency polio immunization campaigns were conducted on 13-16 June in high-risk and border areas of Benin, Burkina Faso, Mali and Niger, followed by additional campaigns in July.

Activities based on economies of scale and tied to cross-border business can still pay their way.