NEW YORK (AFP) - The shock announcement that billionaire philanthropists Bill and Melinda Gates are to divorce after 27 years of marriage has raised questions about the future of their hugely influential charity.

Here's a look at the Gates Foundation, from how it works and what projects it finances, to its impact on the pandemic and how the non-profit may be impacted by the split.

Its mission, and vast budget

The couple say the idea for the foundation came to them as young parents when they read a newspaper article about millions of children in developing countries dying from easily treatable illnesses such as diarrhoea and pneumonia.

In 2000, the Bill & Melinda Gates Foundation was launched to fight disease and poverty around the world. In the United States, an initial focus on providing access to computers and the Internet was expanded to improving education in general.

With 1,600 staff in offices around the world, the Gates Foundation gives away roughly US$5 billion (S$6.7 billion) each year in areas like global public health and development.

The foundation says it has spent US$54.8 billion since its inception.

More than US$2 billion has gone towards fighting malaria alone, with the aim of eradicating the mosquito-borne disease "within a generation".

The charity has also contributed several billion dollars towards a global campaign to end polio through the widespread immunisation of children. It donated more than US$50 million during the Ebola outbreak in 2014.

Dozens of other programmes it funds include nutrition, sanitation, maternal and newborn child health and agricultural development.

Battling the pandemic

Last year, the foundation pledged about US$250 million to help fight the pandemic, with some of the funds channelled to the distribution of life-saving doses of Covid-19 vaccines to parts of Sub-Saharan Africa and South Asia.

The money also went to testing, personal protective equipment and support of overwhelmed health services, particularly in developing countries.

It was also key in forming Covax, a global programme to help supply vaccines to the poorest countries.

In total, the foundation says it has spent some US$1.75 billion fighting Covid-19 since the start of the pandemic.

It found itself embroiled in controversy though after it was accused of pushing Oxford University to sign an exclusive agreement with AstraZeneca for its vaccine rather than donate the rights to any drugmaker.

Who runs the foundation?

Bill, 65, and Melinda, 56 are co-chairs of the charity while Mr Warren Buffett is a trustee. The chief executive is Mark Suzman.

In its early years, when Mr Gates still ran Microsoft on a daily basis, Mrs Gates was seen as leading the foundation.

In 2008, Mr Gates moved to a part-time role at Microsoft to devote himself to the foundation. Last year, he left his board positions at Microsoft and Berkshire Hathaway for the same reason.

It is hard to say which, if either of them, is more influential.

In her 2019 memoir, The Moment Of Lift, Mrs Gates wrote that they argued over who would write the foundation's annual letter, which Mr Gates had typically done.

"I thought we were going to kill each other," she said. They have been writing it jointly since 2014.

Where does the money come from?

The Gates transferred some US$20 billion in Microsoft stock to the foundation in its early days.

In 2006, Mr Buffett announced that he would donate the bulk of his fortune to the foundation in the form of shares in his company Berkshire Hathaway.

Four years later, Mr Gates and Mr Buffet launched the Giving Pledge initiative, which encouraged the rich to donate at least 50 per cent of their wealth to charitable causes, including the Gates Foundation.

More than 200 prominent people have made the pledge to date.

The foundation has an endowment of more than US$46 billion.

At the end of last year it had a vast portfolio of stocks, dominated by Berkshire Hathaway and also including Walmart, Caterpillar, US company Waste Management and the Canadian National Railway Company, according to Investopedia.

Does divorce threaten the foundation?

Mr Gates, the fourth-richest man in the world with a fortune valued by Forbes at US$130 billion, and Mrs Gates have pledged to continue working together for the foundation.

But their divorce could create new questions about their wealth, most of which has yet to be donated to the foundation, despite co-creating the Giving Pledge.

The future of the Gates Foundation could depend on the financial terms of the divorce, which are still unknown.

Mrs Gates might want to follow the example of Ms MacKenzie Scott, who quickly gave away an estimated US$6 billion after her divorced from Amazon founder Jeff Bezos in 2019 and is now a powerful independent philanthropist in her own right.