In the event of a plague threatening to wipe out all of humanity, the first thing to do is stay calm. Plagues have swept the planet time and time again, and though it nearly always sets civilization back a few years, it’s nearly always survivable. With your help, a few more people may survive as well.
Detecting the threat:
Obviously, disease is fairly common through the world. In order to be classified as a global threat, the disease must meet the following qualifications:
Appear in multiple countries almost simultaneously.
Kill over 10% of those infected.
Have no known cure (or a cure that is so ridiculous, random, or rare that it may as well be incurable for the common individual).
If the infected die and then begin to reanimate, and it can be determined that the individuals are now undead, see Zombies.
Analyze the threat:
Determine how infectious this disease is.
Can it be transmitted through the air, or only bodily fluids?
How close does a person have to get to an infected individual to acquire the disease?
Is it being carried by insects or rodents (or birds, aliens, ghosts, etc)?
Determine how lethal the disease is.
How quickly do people die from it?
Can the symptoms be treated, thus prolonging the life of infected individual even without a cure?
If an area was quarantined, how long would the quarantine have to remain in effect before everyone inside died and the rest of the world was safe?
Does the disease affect behavior at all? Rage viruses can often be confused with zombies and lead to incorrect treatments.
What causes the disease?
Alien life form (could be any of the above)?
How did the disease begin?
Did a mad scientist create it in order to take revenge for not being asked to prom (or because of any other vague, undefined reason)?
Did explorers venture into an unexplored portion of the world and bring back a terrible, never-before seen illness that likely would have escaped long before if it was actually as infectious as it seems)?
Did an archaeologist disturb an ancient tomb and inflict a curse on the world (perhaps by knocking a vase off a display, thus angering the ghost of the individual that was tasked with keeping the tomb clean)?
Did you redirect an asteroid to land on one of the United State’s enemies, only later realizing that it contained alien life forms that are now infecting the planet?
Combat the threat:
Eradicating the disease will likely prove as challenging as it was to determine the cause. Once you have reached this stage, there are multiple options.
IF: The disease is simply a never-before-seen virus, bacteria, protozoa, parasite, or other Earth-native agent, contact the CDC through ordinary means and alert them to the threat. There’s a very small chance that they haven’t already seen it, but it never hurts to be prepared. Be on standby to travel to distant parts of the world (deep jungles and mystical mountaintops are most likely) to find components for the cure.
IF: The disease is an alien life form, see Aliens.
IF: The disease is caused by the supernatural, see Supernatural.
IF: The disease is caused by something that isn’t listed above, alert Washington so that key individuals can evacuate the planet.