I agree with what your saying. Theres still a lot of unknown with the anti-virus etc. I would assume,, and I know this is asking a lot from a goverment entity, that they would do a titre test after the anti vac. I know I had to have 1 for several vaccines I got when I was on the line. One of the things I was referencing is that there's no mention on how to deal with it. There's things in the package I dont see that means either a they don't know they don't know, or b its deliberately vague for CDC to fill in the gaps. Which based on somethings im not seeing there either, leads me to believe that there's things they don't know they don't know also.
I've seen more then a few conflicting accounts on herd immunity and the anti virus In general. So it's still a huge grey area.
Something else that isn't addressed is what states have a quarantine in place order for other states. How does that factor in to their plan? I think Hawaii is one for example. Florida, the cruise capital of the world had a ban on NY and some other travelers for while, as another example.
Its a good start from what I'm seeing but this is all up to the CDC and when they decide to do something. Even then it won't be instantaneous as I think it was Royal that said it will take at least 30 days if not longer to get full crews back to the ships, the ships themselves ready, and this is also assuming the Coast Guard doesn't get involved, as there certain time frames that may get exceeded and then they have to physically inspect every ship, and credentials of every mariner to make sure they still meet or exceed the requirements. The longer a ship is idled, the longer it takes to get them back in service. What there doing now, running them to the islands will help but if they park them, 90 days just for the CG side wouldn't be out of the equation.
Some of the reporting coming out reporting on the progress of the clinical trials for some of the candidate vaccines speaks to the vaccine producing antibodies in the volunteers, and how strong those antibodies are, etc. i.e. that the person appears responsive to the vaccine. So that is one aspect of work being done in the clinical trials underway. Presumably it would be one of a set of a pre-determined set of criteria that would need to be met before a vaccine could be considered for approval.
For many of the routine vaccines people get there are titre tests available, but they may not routinely be in use in some places. For example, for me, there is a question about the Hep A and B vaccines I received and whether they were sufficient due to some irregulaties in the series I got. Instead of having my titres measured, my doctor is just having me start over and be revaccinated for Hep A and B as if from scratch.
One can't easily get covid antibody testing here to find out if you were previously infected, but in other areas it is more widely available.
And yep, the state or jurisdictional quarantine issues will be a factor. The US doesn't allow entry at all from certain countries for tourist purposes. Various states have quarantine requirements for visitors from various places. Countries have "avoid all travel" and/or "avoid cruises" advisories in place. All of these will impact passengers' ability to get to the embarkation port and in some cases will outright prevent it.
Compounding the issue is the ability for travellers to obtain travel and/or travel medical insurance that will sufficiently cover them for general travel needs and for covid-related ones specifically. That may be difficult, cost-prohibitive, or impossible to obtain.
And you are quite correct about the issue of getting the ships themselves, including their crews, ready to sail. Beyond the very practical issues of getting the ships ready [they've been closed down for months and it will take time to get them "open" again], there are regulatory hurdles, and the issues of crewing, which has HR, immigration, quarantine, and training, and travel among other issues to navigate. I don't know how crew visas are issued, but US embassies and consulates in many locations are not back to issuing any kind of visas yet, with some barely or only recently open for American Citizen Services; others may still be closed. And some crew members may have their own passports and such they may need to renew and encounter challenges locally with that. Lots of spinning wheels = a good chunk of time.
There is video one of the senior officers of one of the (IIRC Princess) ships took a few months ago. They were waiting at sea with a number of other ships to be able to repatriate crew. He took viewers on a walking tour of the ship, showing how they had closed off many of the different areas: he basically took the camera along as he did his nightly inspection of these areas. They were all passenger areas. So places like the bars, pubs, restaurants, casino. Covers were over things, furniture rearranged, lights off, etc. Kind of spooky. In other areas they had pulled things into them and were using them for storage and such. Needless to say, all that would have to be "undone" to return it to a guest-usable and ready space, in addition to whatever renovations needed to be done as part of new safety protocols.
SW