The 2015 Gates annual letter projects that "the lives of people in poor countries will improve faster in the next 15 years than at any other time in history." (Bill and Melinda Gates Foundation)

Bill and Melinda Gates have outlined their vision of what the world will look like 15 years from now, and it is confidently optimistic: The number of children dying before the age of 5 will be cut in half; polio, guinea worm and river blindness will be wiped off the face of the Earth; and the African continent will be able to feed itself.

The couple announced those goals Thursday in their foundation’s annual letter — which over the years has become a sort of State of the Union for the development world and has become influential in shaping the agendas and framing the debates for the greater global aid and health communities.

In a joint interview with his wife before the letter was released, Gates said he hopes their foundation’s new commitments will serve as a catalyst in the coming years for other work that ensures every person on the planet has his or her basic needs met.

“Does that kid have a chance to have a good education? To not suffer from malnutrition? These are the primary issues we’re trying to point resources at,” Gates said. While philanthropy provides only a small fraction of the money going toward this kind of work, he added, much of “the high risk, the innovation comes from that element.”

Since the Bill & Melinda Gates Foundation was created in 2000, it has shaken up the world of international aid with its focus on measurable goals (often lives saved) and its ability to rally large and diverse groups of stakeholders to work together toward a common goal.

(GAVI Alliance/Bill and Melinda Gates Foundation)

Some organizations and individuals have questioned the foundation’s priorities over the years, arguing that it is drawing resources away from worthier causes, and expressed worry that its mammoth size — its endowment is $42 billion — is stifling a diversity of views because it funds so many projects in certain fields.

But even its critics have found it hard to argue with its success in areas such as childhood vaccines — an effort that has managed to bring immunizations to even the most remote parts of the world, saving millions of lives.

This year’s letter is broader in scope than previous letters that were often focused on a single idea or area of interest. In it, the Gateses reaffirmed their focus on child and maternal health and communicable diseases such as malaria and HIV, but they also signaled that two other areas — agriculture in Africa and technology in banking and education — would become major priorities in the coming years.

Once considered an unrealistic near-term goal, the idea of Africa becoming self-sufficient in its food supply is now an objective that a growing number of experts believe may be possible. The debate has been about how. The World Bank, in a report published in 2012, outlined how it believes this could be achieved if different countries trade with one another instead of importing from the outside.

For the Gateses, the answer is science. They believe that African farmers could theoretically double their yields using new types of fertilizers and better seeds.

On banking, Melinda Gates said mobile finance is important not only for economic reasons but also for health ones. She said the foundation will put a special emphasis on making sure mobile phones reach women.

“It’s so important because if they get an extra dollar in their hands they are 90 percent more likely to plow it back into the health of their families. They are the ones often dealing with the health shocks if the child gets malaria or otherwise gets sick,” she said.

(Bill and Melinda Gates Foundation)

The Gateses also emphasized the importance of getting individuals involved in efforts to improve the lives of people in poor countries. They announced the launch of a new campaign called Global Citizen that will serve as forum that brings together anyone who wants a voice in the matter.

“Having individuals stand up and say I care about the rest of the world and I care about these inequalities and I’m going to hold my government accountable for what they do — that’s what we’re hoping will happen,” Melinda Gates said.