How a six-in-one vaccine could soon help the world get rid of polio for good

Polio eradication is a delicate dance. And one of the biggest challenges facing the people trying to choreograph its final steps is how to phase out use of oral polio vaccines.

The oral vaccines have brought the paralyzing viruses to the brink of annihilation; so far this year there have only been six cases detected, five in Afghanistan and one in Pakistan. But a feature of the oral vaccines — that the live viruses in them can spread and on rare occasions regain the power to paralyze — means that while they are in use, the world will never be free of polio.