It appears that the new strains are so contagious and changing so rapidly the idea of contact tracing, natural immunity, herd immunity, isolation, and maybe even vaccination mean nothing. I know several people who are on their third infection by now and no telling how many people actually have it at any given time. We cruise last month, and we only know of two families that reported infections after the cruise but of course a lot may have just stayed silent about it.
I would like to know how many people test positive before a cruise. This might be a more important measure.