Cruise lines were lying abound infections for years before COVID.
My partner and I went on a Princess cruise in January 2019. Within days my partner came down with signs of Covid. We were on a 21-day cruise. When we got back to the States, Covid news had hit the media airwaves. I believe he had covid then. I also believe other passengers had it then.
They are not known as floating Petri dishes for nothing. No matter what cruise lines tell you.