Microsoft founder Bill Gates and his wife Melinda have said they will donate $10bn (£6.2bn) over the next 10 years to develop and deliver new vaccines.

Mr Gates, speaking at the World Economic Forum in Davos, Switzerland, said the aim was to see 90% of children in developing countries immunised.

Over the past 10 years, the couple's charity has committed $4.5bn (£2.78bn) to the development of vaccines.

The World Health Organization called the commitment "unprecedented".

Mr Gates said that by increasing immunisation coverage in poorer countries to 90% it should be possible to save the lives of 7.6 million children under five between 2010 and 2019.