Let's look at a closed system, the formerly quarantined Diamond Princes: Diamond Princess Crew+Passengers: ~3,533 Infected: ~700 (Infection rate 20%) Mortality rate (Seven dead): <0.2% World average mortality rate: 7.7/1000 yr Expected mortality 1.5 months of ~3533 population: 3.4 Only 2x more people died than expected due to average mortality rates.  Given the older demographic of cruises if deaths occurred in over 70 mortality rate may have been lower than average.