It depends what you qualify as 'serious'. Influenza is one of the most successful and contagious viruses out there, but it isn't usually fatal. It can be, though, for the elderly, children, or people with weakened immune systems. In a place like this, it spreads even more quickly, and we don't have the staff or the supplies to treat everyone as well as I'd like.
You too, Sandry! What sort of a place are you from?