Ragged - just because it hasn't killed anyone you know in real life or caused the death of an unborn baby doesn't mean it doesn;t happen.
As I said before DD2 absolutely fine, DD1 not so good. No she didn't die but it came on so strongly and quickly that she we had to take her to the hospital where she was treated as a priority, I don;t fully recall what happened, but I spoke to DH about this last night and he said it was awful and they gave her everything they could.
I too thought this was just a normal part of CP, she just had it worse than everyone else, until I heard (not on MN) that you can die from CP, it isn't necessarily a harmless disease, yes it is for most people but I think that people should be more aware of the dangers.
And in this case its not just about general social life its affecting, its a trip overseas that has been booked and paid for and would probably cost a fortune to change. Now you could say that her DS could catch CP from a random stranger tomorrow and you;d be right, however why increase the risk if you don't need to.
And to everyone saying about how the advise used to be have CP parties, advise used to be that you could beat your child/wife with a stick as long as its no thicker than your finger - an exagerated comparrison I know but advise changes. My mum was advised to carry on smoking when she had me, andthat a glass a guiness a day was good for her, don;t think I've seent that advise recently.
OP, it has happended, I think you're right to be annoyed and I think you need to sit down with your nanny and explain why you're not happy with what she did and in future she should err on the side of caution. Hopefully your DS has not caught it this time.