The Prime Minister said the money would help save 1.4million lives in the developing world over the next five years.
'Britain will play its full part,’ he said, adding that the money would save ‘one child’s life every two minutes.’
The UK has already pledged £2billion over the next 30 years towards the fund set up by the Global Alliance for Vaccines and Immunisation (Gavi).
This is more than any other nation – including the U.S.
At a conference organised by Gavi in London today, world leaders, charities and philanthropists including Microsoft's Bill Gates were urged to give an extra £2.3billion by 2015.
Mr Gates promised to make a donation of £1billion over the next five years.
Mr Cameron acknowledged that the increased cash for vaccinations - part of the UK's goal of devoting 0.7 per cent of national income to aid by 2013 - would be 'controversial' at a time of cuts in spending on public services at home.
He told the conference: 'At a time when we are making spending cuts at home what we are doing today and the way we are protecting our aid budget is controversial.
'Some people say we simply can't afford spending money on overseas aid right now, that we should get our own house in order before worrying about other people's problems.
'Others see the point of helping other countries to develop, but they don't think aid works anyway, because corrupt dictators prevent it from reaching the people who really need it.'
But the Prime Minister rejected these arguments.
'I think there is a strong moral case for keeping our promises to the world's poorest and helping them, even when we face challenges at home,' he said.
'When you make a promise to the poorest children in the world, you should keep it.'
HOW ABOUT SPENDING OUR TAX-PAYERS CASH ON OUR OWN PEOPLE FOR A CHANGE!