Pandemics have happened through-out our history. The Plague ravaged through Europe for hundreds of years. The Spanish Flu in 1918 was responsible for killing about 6% of the World's population. Pandemics have occured, and will occur again!
What is different today is that now people can travel from one part of the world to another far off part of the world in a day. Notice the Plaque was mostly confined to Europe when people couldn't move around as much as we can today. Then the Spanish Flu spread world-wide when people could move around more freely. Today, one person in Africa infected with Ebola can travel to New York city over-night!
Our cities today are also different from cities in the past. Today our cities have much greater population densities than they once did. One infected person in a city today has a much greater chance of infecting many more people than they could have in the Middle Ages for example.
While now our medical community has more powerful tools and knowledge then they have at any time in the past - they are not miricle workers. Even in the U.S. today, production of vacines for common illnesses is limited. Large scale production of the yearly Flu shots takes up to a year - and this only covers a percentage of our population. And the Flu shot is no where near 100% effective - on average 20% of those immunised can still get the Flu.
So should a novel pandemic occur, it would spread across the globe rapidly. It could then take years for a vacine to be found and produced in enough quanties to do any good. During that time you would be on your own.
Read more on surviving the threat of a Global Pandemic