Just got done defending the good old US of A on Extreame difficulty within 46 days and with fewer than 20.6 million casualties with an open government and got a score of 5,407,819. It was actually pretty easy: I distributed masks left and right with the occasional info campaign (which is effectively "Masks and calmness for everyone!"), the media was nice to me thanks to government type (closed government panic control is nasty hard), then I distributed the cure to infected states once it was available and finally closed my borders completely (to prevent foreign disease spreading (which Extreme Policies doesn't prevent)) and isolated the last few infected states when I noticed only a few infected states were left.
I got to say, this is probably my favorite game in the pandemic series. Whereas the other pandemic games are more luck oriented (good luck infecting Greenland AND Madagascar in Pandemic II... :P), this game has real strategy behind it. The only real problem is that the closed government type, while great at forcing the flu not to spread, can often have an impossibly hard time reducing panic (which is virtually always bad, even though it brings in extra tax dollars). Also, closed government having the option to totally control the media would have been nice.