Five years after the World Health Organisation declared that polio had been eradicated in all but four countries of the world, it is making an aggressive comeback.
More than 800 cases have been recorded this year in Africa - dozens of them in the Democratic Republic of Congo.
This week sees an unprecedented simultaneous health campaign involving more than a quarter of a million health workers in 15 African countries. They are at work administering two drops of polio vaccine to the tongues of millions of children.
Alex Duval Smith joined vaccinators in a remote village of Bandundu Province, in the western Democratic Republic of Congo to learn more about the outbreak.
