A pandemic is not just a health problem. The economic impact can be "profound", a conference held in Singapore heard on Friday.
For example, the 2003 Sars outbreak infected more than 8,000 people and killed 774, but it also cost the world $50 billion.
"There were massive economic consequences for a disease that killed relatively few people," Professor Richard Coker said in his keynote speech to the 9th National Security Conference at the Pan Pacific Singapore hotel.
Warning that pandemics will happen again, Prof Coker, a visiting professor at the Saw Swee Hock School of Public Health, said they result in "irrational individual, corporate and national behaviour".
"They may result in limited public health consequences, but profound economic, social and political consequences," he said.
"These are more likely in highly-developed, interconnected societies."
Health Minister Gan Kim Yong agreed. Quoting World Bank estimates, he said a severe flu pandemic could cost the world $3 trillion, or a 5 per cent drop in global gross domestic product.
The threat of another pandemic is very real, he added, though Singapore is far better prepared to cope with one today than it was a decade ago when Sars hit.
Then, the Republic had so few isolation rooms that "makeshift cabin wards" had to be built.
Public hospitals now have almost 400 isolation rooms.
"There are also 48 infectious disease physicians, triple the number of a decade ago," Mr Gan added.
However, he warned against complacency: "There could be new challenges and we must be prepared to change our plans."