155 countries and territories are switching to a different polio vaccine, in what health officials say is the next step to completely eradicating the disease worldwide.
What will be the big stories of 2016? Four experts offer their best guesses. They worry about Zika virus and malaria. But not all their predictions are downers.
Polio paralyzed Sani Muntari as a child. That didn't keep him from school or off the soccer field. And he's played a key role in making Nigeria polio-free.