At least two million children will die a year if they are not immunised

The US philanthropist told the Times he was "very excited" about the Prime Minister and Chancellor's leadership.

He called on international statesmen to followed their example.

The US$750m (�400m) pledge by the Bill and Melinda Gates Foundation will be spent on vaccines for children in the developing world.

The Norwegian government is also to give �160 million (US$300 million) to the Global Alliance for Vaccines and Immunisation (GAVI).

There is a challenge of keeping world health in front of people, because it is in a sense a tragedy just happening there in the background Bill Gates

Mr Gates told the newspaper: "I have spoken with Tony Blair and Gordon Brown about their commitment and I am very excited about the leadership they are bringing.

"The Prime Minister has talked about Africa as one of his big priorities and I think it is pretty novel that a world leader of a developed country is giving so much visibility to these issues.

"The idea that governments could do a pretty dramatic step-up in their health spending is something I am very excited about."

According to the Global Alliance for Vaccines and Immunisation (GAVI), together with the Vaccine Fund, two to three million children a year will die because they do not get the vaccines which are routine in the developed world.

"There is a challenge of keeping world health in front of people, because it is in a sense a tragedy just happening there in the background," said Mr Gates.

"That is why it is so fantastic that Gordon Brown and Tony Blair are stepping up and saying, 'Let's keep this front of mind'."

Record Pledge

Mr Blair has pledged Britain will press other rich nations to join in writing off debt owed by the world's poorest countries during its presidency of both the EU and G8, while the Chancellor pledged massive new international support to end poverty during a tour of Africa earlier this month.

In 2004, the Bill & Melinda Gates Foundation donated �55m (US$103m) for the development of a tuberculosis vaccine - to the Aeras Global TB Vaccine Foundation.

It was the largest grant ever awarded to the development of such a vaccine.