I sympathise with Martin Heard's suggestion for cruise companies to vet passenger health before embarkation (Health checks should be for passengers too, April 2020 Telegraph letters). In addition to checking for Covid-19, cruise companies could check that passengers can walk to muster stations, see safety notices, hear safety announcements and follow safety instructions. I suspect if cruise companies were to implement such draconian checks, they would lose a significant portion of their clientele.
However, it is not cruise companies that require seafarers to have health checks; that is the responsibility of the maritime regulator IMO. The IMO also has responsibility to ensure passenger safety facilities are fit to use, but paradoxically no responsibility to ensure passengers are fit to use them! Until IMO closes this loophole, cruise companies will continue to transfer responsibility for the welfare of infirm and disabled passengers to ship's staff.