Well if they specify a dress code I try to observe it & so should eveyone...if not forget the lot. I missed almost all the USA ports & barely left the cabin for about a week (including two of the semis). Some people died of it, rumoured between one & six people!
Didn't know about flu jabs in general, I know they exist but that's it. People that had them were less affected for sure.
One REALLY annoying thing was we wanted to use the private area ''The Retreat'',(pool & sunbeds), but they sold all the places to people who arrived the first day (ship takes two days to load/unload).