Microsoft tycoon Bill Gates calls for 'vaccine equality'

Microsoft tycoon Bill Gates has pledged $1bn to help vaccinate children around the world against preventable diseases like pneumonia.

He is hosting a summit in London where countries are being asked to give an extra £2.3bn ($3.7bn) by 2015 for child vaccines.

The Global Alliance on Vaccines and Immunisation (Gavi) says this could help save four million lives in four years.

Gavi is a health partnership of governments, businesses, and bodies including the World Bank, Unicef and Mr Gates' personal foundation.