https://www.nbcnews.com/news/us-news/nearly-50-royal-caribbeans-symphony-seas-cruise-ship-test-positive-cov-rcna9346
My point is that if you gather many people in a tight space - where we are all together for long periods of time, eating together, using the same bathrooms, breathing each other’s air for 8 hours every day, going out into the world and coming back together time and time again: people are going to catch and spread Covid.
It is still not safe to force RTO, even with the best of precautions.