I have an Autoimmune Disease and I am an essential worker as a SS teacher who still has to teach in person. So I am going to get the vaccine as soon as it is available as long as the reliable drs and scientist say it is good... not just a certain politician pushing it .. In Colorado I am on the list they say can get the vaccine early, only the medical staff are ahead of me. But I will not be going cruising or even vacation out of my state till I get it. I cancelled many of my trips this summer and only did the camping ones in Colorado to be safe.
I think countries are going to be the ones who will enforce the vaccine issue on the cruise ships, that is something many countries already require when visiting.
Also another issue, the testing on the vaccines have not been done on children yet so it will be even longer before they approve it for children. So I could see the cruise ships saying adults must have it but children do not since they will not be available even longer after it is available for adults.
Or something else they could do give a special wrist band to people who had vaccines so they do not need to wear masks, while all those who did not have one has to wear a mask.
(On a separate issue
jane01jp please be kind to those of us who have to work in person and put our lives on the line.)