Awa Coulibaly Samake slips two plastic bags over her hands, pulls a pair of old socks over the top, and puts the finishing touches to her do-it-yourself recipe to combat germs.

She is shaping a sticky plaster-like mixture into a sweet-smelling sphere. They are low-cost soap balls and Coulibaly is soapmaker-in-chief in the Nafadji district of Bamako, the capital of dust-blown Mali. It is one of dozens of poor countries where, health experts say, handwashing with soap can have the transformative effect of a vaccination.