The almighty CDC has given ship cruise lines their list of operating rules if they want to operate out of US ports.

This link will take you to the article. But, surprisingly there is nothing about vaccinations. Doesn't matter if you have shots or not, the rules are super-stiff. Doesn't seem like it would be much fun if you have to abide by the rules. CDC has also warned cruise ships they will be "checking on them", either in person or via remote cameras. Masks...masks...masks! All the time, except in your own cabin. No buffets. You can only remove mask to put food in your mouth, but then quickly replace it, apparently. 

We have been on a couple cruises and they were fun. You would have to be recently release from prison solitary confinement to call cruising under the new rules as "fun">

Also, CDC is encouraging cruise lines to come up with something like shocking dog collars to "warn" passengers when they are stretching the rules.

Was Dr Josef Mengele the first director of the CDC? Or was there someone before him?

Here's link:

https://www.cruisecritic.com/ab/agents/variation-a/news/6095/?et_cid=3428455&et_rid=115175032&et_referrer=TripAdvisor