People aboard both ships are being given health screenings, and those with suspicious symptoms are being tested for the virus that has quickly spread throughout mainland China and beyond.

Concerns about potential infection among thousands of passengers at sea exposes the vulnerability of cruise ships to viral illnesses, like the coronavirus. The threat also raises questions about the durability of Asia’s booming leisure cruise industry, which counts the elderly as among its most loyal customers.

Older people are especially susceptible to the Wuhan coronavirus — China’s National Health Commission said Tuesday that 80% of all fatalities in mainland China were over the age of 60.