Not much strumming through the intro, verses go something like

D U D U D UM D UM D... UM D
D: Down
U: Up
DM: Down/Muted
UM: Up/Muted

Hope this isn't to messy, it should work as a reference. It's syncopated by the way so if you tap the pulse against the song you'll see that the stress (downstrokes) rarely falls on the beat.