I keep hearing/reading that but at the same time, I've heard/read nothing about anyone that's had it twice (I know there was a report early on but IIRC, the lady tested negative in the end)
I've read a lot about a "temporary" immunity but again, nothing concrete about how long it lasts. There is also a belief amongst some that, although you won't be immune, they believe that a second infection won't cause such bad illness (would post links to these but it was ages ago and can't remember where I saw them).
Truth is, no one seems to know a lot about it or it's effects which is a little concerning.