I'm convinced there's an underlying reason somewhere why a proportion of people on a cruise succumb to a virus, whereas others don't.
We recently went on our first cruise, a river one, and by 4 days in about 50% were coughing and spluttering. You could hear them in the dining room, in the bar, on the coaches and several of them were having food brought to their cabins and left outside in the corridor afterwards.
DH and I were sure we'd pick up something, but we had a lucky escape. The only thing we could think is that we travel on ferries across the Channel four or five times a year so our bodies are somehow used to the air con!! (You can tell I'm no scientist.)
What I'm saying is, that if you're on a cruise with a virus you might catch it or you might not.