Endorsing vaccines as the world’s most cost-effective public health measure, Bill and Melinda Gates said Friday that their foundation would more than double its spending on them over the next decade, to at least $10 billion.

The change could save the lives of as many as eight million children by 2020, Mr. Gates calculated. He said he hoped his gift would inspire other charities and donor nations to do the same.

“Vaccines are a real success story,” Mr. Gates said in an interview before the announcement, which he made at the World Economic Forum in Davos, Switzerland. “The cost is tiny, and yet it saves more lives than any other component of a health care system.”

Julian Lob-Levyt, the executive secretary of the GAVI Alliance, a partnership among drug companies, health agencies and charities bringing vaccines to poor countries, said he “hugely welcomed” the announcement.