A genetically engineered virus is easier to make and could kill more people than nuclear weapons - and yet no country on Earth is ready for the threat, Bill Gates warned world leaders Saturday.
No one on his panel at the Munich Security Conference argued with him.
''The next epidemic has a good chance of originating on a computer screen,'' said Gates, who made a fortune at Microsoft, then spent much of it fighting disease through his global foundation.
Whether ''by the work of nature or the hands of a terrorist'', Gates said, an outbreak could kill tens of millions in the near future unless governments begin ''to prepare for these epidemics the same way we prepare for war''.
His co-panelists shared some of the same fears.
''Disease and violence are killing fewer people than ever before, but it's spreading more quickly,'' said Erna Solberg, the prime minister of Norway. ''We have forgotten how catastrophic those epidemics have been.''
She recalled the Black Death, which she said killed more than half her country's population and created a 200-year recession in Europe.
''It's not if, but when these events are going to occur again,'' said Peter Salama, executive director of the World Health Organization. ''We need to ramp up our preparedness.''
Gates, who founded the Bill & Melinda Gates Foundation with his wife in 2000, has been worrying about the world's ability to stop a deadly pandemic since Ebola killed thousands two years ago, while governments and militaries struggled to stop it from spreading through West Africa.
''NATO countries participate in joint exercises in which they work out logistics such as how fuel and food will be provided, what language they will speak, and what radio frequencies will be used,'' Gates wrote in 2015 in the New England Journal of Medicine. ''Few, if any, such measures are in place for response to an epidemic.''
He took the same message to Reddit a year later, when a commenter asked which technologies the world was better off without.
"I am concerned about biological tools that could be used by a bioterrorist,'' Gates wrote. ''However the same tools can be used for good things as well.''
'Easier to engineer'
Before his panel on Saturday, Gates told The Telegraph, ''It would be relatively easy to engineer a new flu strain'' by combining a version that spreads quickly with one that kills quickly. Unlike a nuclear war, such a disease would not stop killing once released.
At Munich, Gates ran down all the ways that the world's great powers were unprepared - governments out of touch with the companies that make vaccines, international health departments out of touch with one another, and militaries that may not have considered responding to a biological threat.
''Who's this alternate group that's going to deal with the panic?'' Gates said. ''Who's got the planes and the budget? Maybe the fire department?''
While some others on the panel discussion - ''Small Bugs, Big Bombs'' - focused on the threat of natural diseases, Gates called for ''germ games'' simulations, better monitoring to spot outbreaks early, and systems to develop vaccines within weeks - rather than the 10-year lead time he said was more common.
''We need a new arsenal of weapons, antiviral drugs, antibodies, vaccines and new diagnostics,'' he said.
The Centers for Disease Control and Prevention's website lists seven agents - including anthrax, plague and bleeding fevers such as Ebola - as potential ingredients in a bioterrorist's cookbook.
The center's sections on surveillance and ''planning for all bioterrorism'' cite research papers that are mostly more than a decade old.
In his New England Journal of Medicine article, Gates said the United States's last epidemic simulation took place in 2001.
At the end of President George W Bush's administration, a bipartisan report accused the US government of doing too little to address the threat of bioterrorism.
Two years into Barack Obama's presidency, a congressional panel gave the government an 'F' in preparedness.