Okay, but percentage of infection wise, none of these technically met the requirements to be considered a true pandemic. Heck, the Bubonic Plague was only an epidemic, and it wiped out way, WAY more people than H1N1 ever did. I am well familiar with the more recent history of pathogens, but the problem looks like this...
In any given population, any potentially fatal disease will kill (A) people, infect and inoculate (B) people, infect (C) people who will carry it as a host, and not be contracted by (D) people. What relative numbers those variables represent can vary widely. But lets take a worst case kind of disease... septicemia.
Speticimea, even with immediate medical treatment (within 24 hours of contraction) has a fatality rate averaging at 10%. If it is NOT treated immediately (and keep in mind, it's not uncommon for people to die on the same day they were infected, before any symptoms even appear), the fatality rate rises to 99-100%. It has an incredibly short incubation time, and is highly infectious. So... for such a disease, group A will be very large, even in a place where proper medical treatment is possible, group B will be either tiny or large, depending on access to medical treatment, group C will be nonexistant in any case, and group D will likely be infinitesimally small, because it spreads so easily.
Released into a small, self contained population, it will quickly run it's course: the survivors will be fine within three days, and everyone else would be dead. That's kind of how things went in the Middle Ages, but even then, it swept half the length of the globe, though in a fairly narrow channel. But were an outbreak of septicemia to happen TODAY, the results would be, literally, apocalyptic. Back then there were three hundred million people, MOST of whom had never even left the villages they were born in. NOW, we have 6 billion, and many of us travel across continents in a matter of hours on a daily or weekly basis. The same holds true with any deadly, easily transmittable disease. And if it should happen to have a longer incubation time or less obvious symptoms than the disease I have mentioned? Well... kiss your ass goodbye. Of course, most infections are not nearly so virulent... but my point is that, with so packed a planet, the first one that IS that comes along is likely to kill the vast majority of us, simply because of how easily people in large, mobile groups spread illness.