Yes! On our cruise last June, I was really worried that one of my 3 kids would get sick. If one of my kids gets sick, they usually spread it to my other kids and it stays in our house for like 2 weeks.
So a few weeks before we sailed, we started giving the kids gummy vitamins with echinachea. And I stopped taking them to indoor germy places (like my gym daycare, indoor mall play areas, etc.) I also made sure the kids washed their hands a few times a day and before all meals and snacks. We kind of cocooned ourselves a week before the cruise. And it worked.
Our next cruise is in February, which has me a little more worried since it's winter. But my plan will be the same--start the vitamins, no indoor play areas, etc.
Good luck!