Bill Gates, the Microsoft cofounder who has recently been focusing most of his efforts on philanthropy, joined several world leaders to pledge billions for vaccines for children in poor countries.

"This is absolutely human generosity at its finest," Gates told reporters Monday at the Global Alliance for Vaccines and Immunization conference in London.

"For the first time in history, children in developing countries will receive the same vaccines against diarrhea and pneumonia as children in rich countries," Gates, who founded the alliance, said, according to Reuters.

Gates and several international donors pledged $4.3 billion to buy vaccines to protect children in poor countries against potentially fatal maladies like pneumonia and diarrhea.

British Prime Minister David Cameronpledged $1.3 billion and said despite his nation's budget cuts, this cause is a no-brainer.

"Frankly, the idea of children dying from pneumonia and diarrhea should be absolutely unthinkable in 2011," Cameron said from the conference. "But for many parents in the developing world it is a devastating reality."

The global alliance has already vaccinated 288 million children in 19 countries and hopes to immunize 243 million more by 2015. It wants to broaden its reach in coming years by going to 26 additional countries.

"Today is an important moment in our collective commitment to protecting children in developing countries from disease," Liberian President Ellen Johnson Sirleaf said. "But every 20 seconds, a child still dies of a vaccine-preventable disease. There's more work to be done."