Hello Tobias.
First: the swine flu it's over, according to WHO. Second: the world has 7 billions of people, thus the pandemic must to be highly transmissible. Third: the science and medicine are advancing, more each year. I think that this is hard. It would be easier a century ago, but not today…
Update:
You said about the Black Death. Look what Wikipedia says about this pandemic:
Black Death, started 14th century. The total number of deaths worldwide is estimated at 75 million people. Eight hundred years after the last outbreak, the plague returned to Europe. Starting in Asia, the disease reached Mediterranean and western Europe in 1348 (possibly from Italian merchants fleeing fighting in the Crimea), and killed an estimated 20 to 30 million Europeans in six years; a third of the total population, and up to a half in the worst-affected urban areas. It was the first of a cycle of European plague epidemics that continued until the 18th century. During this period, more than 100 plague epidemics swept across Europe. In England, for example, epidemics would continue in two to five-year cycles from 1361 to 1480. By the 1370s, England's population was reduced by 50%. The Great Plague of London of 1665–66 was the last major outbreak of the plague in England. The disease killed approximately 100,000 people, 20% of London's population.
If a black death pandemic happen today, would be very bad too, but would not have the same effect that it had in 14th century. But maybe the disease would spread faster, regarding the actual population of the world. Anyway, today the science is much more advanced than years ago…
Good Luck and Happy New Year!