Yes, it could be very uncomfortable if you go back to playgroup and say something based on that assumption and they are actually immunised. The new whooping vaccine is said to be only 30% effective as it misses two of the main strains. 70% of the 30,000 cases of whooping cough that occurred last year were in people who were immunised, of the 30% who weren't, most of them were adults. So it can be a dangerous assumption to think that just because some is vaccinated they can't get it and only people who are unvaccinated do.

If on the other hand, the health service told you that they were unvaccinated, that is an incredible breach of ethics, as they should be medical in confidence. It's one thing to inform you of an outbreak, it's quite another to give specific details of someone's medical past.