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.
"We must make this the decade of vaccines," he said in a statement.
"Vaccines already save and improve millions of lives in developing countries. Innovation will make it possible to save more children than ever before."
He said money was needed to make the most of new vaccines now becoming available, including ones against severe diarrhoea and pneumonia.
Melinda Gates added: "Vaccines are a miracle. With just a few doses, they can prevent deadly diseases for a lifetime.
"We've made vaccines our number one priority at the Gates Foundation because we have seen first hand their incredible impact on children's lives."
Margaret Chan, head of the World Health Organization, said it was an unprecedented contribution and urged governments and private donors to add to the initiative.
"An additional two million deaths in children under five years could be prevented by 2015 through widespread use of new vaccines and a 10% increase in global vaccination coverage," she said.