The chances of something happening on the other side of the world directly affecting us here are pretty slim.
With globalization, though, this is changing. What happens in East Asia today may very well have a huge impact on us tomorrow. And it may even kill us.
These days, diseases such as the flu can travel globally in a very short period of time. And now researchers at the Harvard Initiative for Global Health at Harvard University predict that as many as 81 million people in the world could die in one year if a very contagious form of the flu spread in modern times.
Just to put that number in perspective, the total number of human deaths from all causes last year was 58 million.
Pandemics -- global disease outbreaks caused by viruses or other organisms -- usually occur because the type of organism is new. Our immune system has trouble fighting it, as it has never seen it before.
The study is published in the current issue of the British medical journal Lancet.
"We wanted to see what the actual numbers might look like," said Dr. Christopher Murray, professor of public policy and social medicine and director of the Harvard Initiative for Global Health.
To do this, the researchers applied historical death to current populations to see what would have happened if a virus spread around the globe in 2004. They expected a death toll between 15 million and 20 million.
What they found out was that between 51 million and 81 million individuals would die in current times if a pandemic like the 1918-20 flu hit -- and 96 percent of these deaths would be in developing countries.
With the avian influenza epidemic in birds and the few hundred cases recorded in humans, some fear that a bird flu pandemic is approaching. However, the onset of such an event is difficult to predict.
"Flu pandemics are just like earthquakes," said Kenneth Hill, associate director of the Harvard Center for Population and Development Studies at Harvard University and co-author of the study. "Major outbreaks are by no means regular. And you can't predict that the next one will be this year or the next.
"All you can say is that based on historical records and probabilities, a major one is likely to happen," Hill said.
Experts say that, on average, flu pandemics happen every 30 to 40 years, and it is not possible to say how serious a new pandemic will be. It depends on the characteristics of the new virus.
The 20th century saw three main pandemics -- in 1918, 1957 and 1968. The 1957 and 1968 pandemics each killed 1 million to 2 million people -- a relative drop in the bucket. The one in 1918 killed more than 20 million and is often used as a theoretical upper limit for future pandemics.
"Since it is hard to say if future ones will be more like a 1918 or a 1957 pandemic, it certainly makes sense to be prudent and do what we can to prepare ourselves for a pandemic," Murray said.
"Unfortunately, we can't avoid pandemics," Murray said. "But we can reduce the number of cases that occur and reduce the number of deaths."
One interesting result of the study was that it showed a large variation in how different countries around the world would be affected by the pandemic. And poorer countries would likely bear the brunt of the catastrophe.