Image caption Many developing countries cannot afford life-saving vaccines for children

Countries have pledged an unprecedented $4.3bn (£2.6bn) to help vaccinate children against preventable diseases like pneumonia.

The Global Alliance on Vaccines and Immunisation says this funding milestone will save more than four million lives in the next four years.

The donations exceeded expectations - GAVI asked for $3.7bn.

The UK promised $1.3bn, and Microsoft tycoon Bill Gates said he would give $1bn to the campaign.

Other donations announced at the London summit included $677m from Norway and $450m from the US.

Australia, France, Germany, Italy, Sweden and The Netherlands also promised to contribute.

The UK has already committed more than any other nation - £2bn over 30 years.

The extra £814m comes on top of the UK's existing commitment of £680m between 2011 and 2015.

The cost-effectiveness of immunisation is likely to be one of many arguments put forward at the conference Fergus Walsh , Medical correspondent, BBC News Surviving childhood in Sierra Leone

'A promise'

Prime Minister David Cameron said there was a "strong moral case" for keeping pledges Britain had made to the developing world, no matter the economic circumstances at home.

"Today we come together because we have the chance to save another four million lives."

He said the idea of children dying from pneumonia and diarrhoea should be "unthinkable" in 2011.

"To those who say fine but we should put off seeing through those promises to another day because right now we can't afford to help: I say - we can't afford to wait."

Two million under-fives die from pneumonia alone each year despite the existence of a vaccine to protect them.

It is estimated that three times as many children aged under five die from pneumonia and diarrhoea than from malaria and HIV/Aids combined, despite new vaccines being available to help prevent such deaths. However, many developing countries cannot afford them.

'Make-or-break'

Drugs company GlaxoSmithKline last week agreed to sell a vaccine for diarrhoeal disease at cost price to poorer nations, and some other firms have since made similar moves.

GAVI has already rolled out a range of vaccines to children in 72 countries but the organisation says it needs the extra money to vaccinate even more children against pneumococcal disease and rotavirus.

Media playback is unsupported on your device Media caption Microsoft tycoon Bill Gates: "In the achievement of vaccine equality this is a very important day"

Resources will also be spent on trying to reach millions of the poorest children who are missing out on basic vaccines against diseases such as measles, whooping cough and tetanus.

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

The philanthropist Mr Gates said: "I just want to thank everybody for this incredible milestone. Four hours is a long time but if you can save four million lives in four hours it's well worth every minute.

"For the first time in history, children in developing countries will receive the same vaccines against diarrhea and pneumonia as children in rich countries."