Question about getting Whooping Cough twice

Just wondering if anyone knows where I could find information on the likelihood or stats relating to the chances of a fully immunised toddler/pre-schooler getting Whooping Cough twice?? i.e. contracting it in a mild form in 2011 at 2.5 years old and then re-contracting it again a year later.

I'm about to try and google it but because it's a pretty obscure question, I don't like my chances of finding anything much and thought I'd tap into the awesome amount of knowledge in BB :)

TIA.

I'm not sure if she was immunized but my sister had whooping cough several times.

Yeah I have discovered that the vaccine is only against one strain of WC and the disease has apparently been mutating and is pretty good at getting around the vaccine which is why there is such a lot of it around in the community atm. Just wondering what the actual numbers are on re-infection?