In 2006, famed investor and businessman Warren Buffett pledged to give away 85% of his fortune to charitable organizations, with the most sizable chunk, valued at the time at $31 billion, going to the Bill and Melinda Gates Foundation, the largest private foundation in the world which tackles worldwide issues related to healthcare and extreme poverty.

At the end of 2016, Buffett wrote a cordial letter to the Gateses, asking to outline what impact his gift has achieved so far. The 2017 annual letter from Bill and Melinda seeks to do just that, calling Buffett’s gift “the biggest single gift anyone ever gave anybody for anything.” 

The main accomplishment of the foundation, according to the Gateses, is their work in reducing children’s mortality. In fact, what Bill and Melinda call “Our Favorite Number” is the 122 million children’s lives that have been saved since 1990.  These are children that would have died had the children mortality rate not gone down. The Gates’s philanthropic work makes a particular emphasis on improving global health issues, with reducing the deaths of kids around the world being a goal that inspired them from the beginning.

“Saving children’s lives is the goal that launched our global work. It’s an end in itself. But then we learned it has all these other benefits as well. If parents believe their children will survive—and if they have the power to time and space their pregnancies—they choose to have fewer children,“ writes Melinda Gates.

In a recent tweet, Bill Gates points to the chart showing how the number of children’s deaths was cut in half, calling it "the most beautiful chart in the world”:

Bill says it was their trip to Africa over 20 years ago that really highlighted the problem for them. 

“As you know, we’d taken a trip to Africa to see the wildlife, and we were startled by the poverty. When we came back, we began reading about what we’d seen. It blew our minds that millions of children in Africa were dying from diarrhea, pneumonia, and malaria. Kids in rich countries don’t die from these things. The children in Africa were dying because they were poor. To us, it was the most unjust thing in the world,” he said.

The Gateses see the reduction of the mortality rate to be indicative of more than just what it shows. The rate also demonstrates the results of other advances in societies that pertain to gender equality, education, nutrition, access to contraceptives, and economic growth. But the biggest reason for the drop in childhood deaths the Gateses attribute to vaccines, which now cover about 86% of the global population. 

global vaccination coverage

The Gates Foundation partnered with businesses and governments to set up Gavi, an organization whose goal is to get vaccines to every child in the world and which has helped immunize 580 million children around the world since 2000.

Bill sees vaccines as a great investment, saying that “for every dollar spent on childhood immunizations, you get $44 in economic benefits.” This is partially due to the money parents save by not taking time off to take care of sick children.  Bill and Melinda Gates

Bill (L) and Melinda Gates, founders of the Bill and Melinda Gates Foundation, take part in a discussion organized by British magazine The Economist about expected breakthroughs in the next 15 years in health, education, farming and banking on January, 22, 2015 in Brussels. (Photo credit: EMMANUEL DUNAND/AFP/Getty Images)

Other accomplishments of the foundation’s work include working with Family Planning 2020, whose goal is to provide 120 million more women with contraceptive access by 2020. It is focusing in particular on South Asia and Africa, where most of the women do not use contraceptives.

What would Bill and Melinda like to see as the culmination of the work? They say it’s the “magic number” of 0

“We want to end our letter with the most magical number we know. It’s zero. This is the number we’re striving toward every day at the foundation. Zero malaria. Zero TB. Zero HIV. Zero malnutrition. Zero preventable deaths. Zero difference between the health of a poor kid and every other kid,” writes Bill Gates. 

Polio is the closest to eradication, with just 37 cases last year. 

As far as their response to Warren Buffett, the Gateses are both thankful to Buffet and proud of what their philanthropic work has accomplished, saying they don't just use the money to send out grants, but are rather “using it to build an ecosystem of partners that shares its genius to improve lives and end disease.”