"Increased investment in vaccines by governments and the private sector could help developing countries dramatically reduce child mortality by the end of the decade," Gates concluded.

Melinda Gates, who heads the couple's Foundation with her husband, said: "We've made vaccines our number-one priority at the Gates Foundation because we've seen firsthand their incredible impact on children's lives."

Vaccine priorities

Since its inception in 1994, the Gates Foundation has spent $4.5 billion on vaccine programmes. The new $1 billion-a-year pledge is $200 million over its current annual outlay for vaccine work.

According to the World Health Organisation, some 79 per cent of children currently receive all three recommended doses of DTP (the diphtheria-tetanus-pertussis vaccine).

A goal of Gate's foundation is to expanded funding is to raise that to 90 percent coverage.

Another goal is to get comparable vaccination coverage among children in the poorest nations for measles, HiB (Hemophilus influenza type B), pneumococcal disease, rotavirus, and, after 2014, a 50 per cent effective malaria vaccine that's now in final human trials.

If those goals are met, Gates says, 8.7 million more children will avoid death from vaccine-preventable diseases.