Very interesting discussion. I am also impressed by the fact that the conversation has been civil compared to other forums I have seen.
Have no Viking experience but do have a lot of cruising history on HAL and Celebrity. Recently got off a 35 day cruise on HAL. Boarded in Boston, test required to board as well as the minimum of 2 shots.No masks required except for crew. Approx. 1,000 passengers with maybe 10-20% wearing masks.
First cases started to show about 3 days in. (First stop was Bar Harbor, a tender port, with folks packed into the tenders and few masks.) They quickly ran out of quarantine rooms and subsequently required those testing positive to stay in their rooms. Finally, after the total number of cases reached somewhere between 100 and 200 people based on the numbers announced by the Captain, they required everyone to wear masks indoors. Still had the geniuses who would remove masks once the lights went off but most folks complied.
After a few days new cases started to level off and then declined to zero about 7-10 days in. Passengers then started to pester those in authority to lift the mask requirement, which they finally did. Surprise! two days later new cases started to appear again.
This was our third cruise since the restart and we try to stay masked indoors and away from large groups (no tenders, no showrooms). So far we have been lucky and will continue to do this as we also continue to travel. No guarantees but masks seem to be a good idea regardless of requirements. Our last HAL trip seems like the perfect experiment.