Melinda Gates 'excited' by pneumonia vaccine
25 January 2011 Last updated at 15:18 GMT
Melinda Gates says she is "excited" by a new pneumonia vaccination that is being rolled out in Africa.
Mrs Gates, along with her husband Bill, set up the Gates Foundation which provides funds to public health organisations around the world.
Estimates suggest that the vaccine could save more than half a million lives a year globally.
The BBC's medical correspondent Fergus Walsh joined Mrs Gates at the Langata health centre in Nairobi, where scores of mothers have been bringing their babies for immunisation.