Technology billionaire and philanthropist Bill Gates has warned that the world may not have seen the worst of COVID-19, and that new and more severe variants could soon emerge.

"We're still at risk of this pandemic generating a variant that would be even more transmissive and even more fatal," Gates told the Financial Times.

"It's not likely, I don't want to be a voice of doom and gloom, but it's way above a 5 percent risk that this pandemic, we haven't even seen the worst of it."

COVID-19 has claimed more than 6.2 million lives so far, and Gates said the virus has proved how underprepared the world was for widespread disease outbreaks. Prior to the spread of COVID-19, the World Health Organization, or WHO, had just 10 people working on pandemic preparedness, according to Gates, and "even those people are distracted with many other activities".

"The current WHO funding is not at all serious about pandemics," said Gates, who called for the establishment of an international team of experts tasked with spotting warning signs and helping to prevent future pandemics.

The proposed initiative, which Gates calls the Global Epidemic Response and Mobilization initiative, or GERM, would be managed by the WHO. Gates has called on global leaders to increase WHO contributions to help establish and run the program, which he estimates would cost around $1 billion a year.

"The amount of money involved is very small compared to the benefit," Gates said.

Since leaving day-to-day operations of his company, Microsoft, in 2008, Gates has spent much of his time funding and leading campaigns to fight diseases, including HIV, tuberculosis, malaria, and polio. In 2015, he gave a prescient lecture on the TED network in which he warned that the world was not ready for the next pandemic.

Gates has now authored a new book, How to Prevent the Next Pandemic, which was published on Tuesday and outlines his vision for GERM. He said that the WHO would be the best body to oversee the program, which would comprise a team of international experts in epidemiology, genetics, data systems, diplomacy, rapid response, logistics, computer modeling, communications, and more.

Some disease warning systems are already in place, such as the Global Outbreak Alert and Response Network, or GOARN, which works under the WHO, but Gates said on his personal blog that this initiative "doesn't have the staffing, funding, or global mandate to tackle every threat".

"We need a permanent organization of experts who are fully paid and prepared to mount a coordinated response to a dangerous outbreak at any time," he said.

Gates hopes that, eventually, the initiative would have the capacity to run exercises he calls "germ games", where computer-aided simulations play out potential scenarios to test for the best responses, similar to war games in the military.