Investors around the world vied with each other on Tuesday to buy into a $1-billion US bond offering to fund vaccinations for children in some of the world's poorest countries.
The securities — the first of their kind — were so popular that there were twice as many bids as there were bonds.
Among those rushing to invest were rock stars such as Bono and Bob Geldof, religious leaders ranging from the Pope to the Archbishop of Canterbury and Chief Rabbi Jonathan Sachs of United Hebrew Congregations of the Commonwealth.
Investors also included the Muslim Council of Britain, the Hindu Forum of Britain and the Network of Sikh Organisations.
Brown said the International Finance Facility for Immunisation aims to raise funds from bond markets over the next 10 years.
"We will ultimately raise an extra $4 billion (US) to deliver life-saving vaccines to children in the poorest countries," Brown said at the launch.
"This will immunize 500 million children by 2015, saving 10 million lives, and help to eradicate polio from the world."
By raising funds this way, bond revenue will become available earlier than would be the case with normal aid budgets.
It costs an estimated $38 US to immunize a child, yet every year 27 million children go without vaccination. The result is that 2.5 million children under the age of five die of preventable diseases every year.
The Global Alliance for Vaccines and Immunisation, co-founded by the Bill and Melinda Gates Foundation, is co-ordinating the vaccination program.
According the Bloomberg.com, the United States has rejected the initiative, preferring to tie donations to the progress made by recipient countries in tackling corruption and opening their economies.