Hopefully technology will one day be able to eliminate potential killers before they start to spread - but until then its necessary to be vigilant to the pandemics that don't differentiate between those with a plan to live forever and those without.

What's the chance of a deadly disease annihilating the world's population? Some of the key factors are:

1. ease of transmission - by contact or air
2. is it infectious before symptoms so that public health measures can be used?
3. how deadly is it? lots of novel flus are no worse than seasonal ones
4. can it be prevented or treated?