Two former passengers of the Diamond Princess cruise ship have died in Japan after contracting the new coronavirus as it ran rampant among the 3,711 people on board.

The two deceased passengers were an 87-year-old man and an 84-year-old woman, both Japanese, according to the Japanese health ministry. Local media reported that they had been taken from the ship to hospitals on February 11 and 12. Both had underlying health conditions, according to local media.

The deaths are the first reported from the cruise ship’s COVID-19 outbreak, which has hit 621 confirmed cases since the first case detected February 1. According to local media, 27 others sickened on the ship are in serious condition. Given that preliminary estimates of the disease’s mortality rate in China is around 2 percent, experts at the World Health Organization said Thursday that they were not surprised by the cruise ship deaths.

The ship’s outbreak is, by far, the largest cluster of cases outside of China. As of Thursday, there are more than 75,700 cases worldwide and over 2,100 deaths. Of those cases, only around 1,070 are outside of China, scattered among 26 countries and the Diamond Princess, which has been docked and quarantined in Yokohama, Japan since February 3. Thus, the ship’s 621 cases account for nearly 60 percent of those outside of China.

As Japanese health officials announced the first deaths, hundreds of other passengers and crew members disembarked after an initial 14-day quarantine ran out Wednesday.

Those from Japan have been advised by the country’s health officials to stay home and monitor their temperature. Approximately half of the initial 2,666 passengers aboard are from Japan, according to Princess Cruise Lines , which is owned by Carnival.

Other countries are flying their citizens home but subjecting them to additional 14-day quarantines upon their arrival.

Next steps

On Sunday, over 300 Americans aboard the ship were evacuated on flights chartered by the US State Department. Fourteen of the passengers tested positive for the virus as they were leaving Japan. All of the travelers are now being held under a 14-day federal quarantine.

More than 100 Americans remained on the ship or in nearby hospitals after Sunday, and the US Centers for Disease Control and Prevention has since barred them from returning to the country for 14 days.

“CDC believes the rate of new infections on board, especially among those without symptoms, represents an ongoing risk,” the agency said in a statement Tuesday.

Japanese health officials have tried to ease concerns by saying that only the passengers and crew who have tested negative for the virus and are showing no symptoms are being allowed to leave. Others who have had contact with confirmed cases are being kept on board for extended quarantines.

But outside health experts are skeptical that the measures are enough to curb the spread of the virus. For one thing, recent reports suggest that people showing no clear signs of infection may still be able to spread the virus. Moreover, the quarantine efforts on the ship clearly failed to contain the virus and have been heavily criticized. Dozens of new cases have still been reported in recent days.

As the health ministry announced the two deaths Thursday, it added that two additional health officials had contracted the virus while aboard the ship, according to Reuters. That brings the number of infected quarantine workers to five.

Princess Cruises, meanwhile, said that once the Diamond Princess is emptied, it will be fully sanitized and dry docked for a short period, according to a report by The Wall Street Journal. The company said the ship will remain in Japan and return to service on April 29 for the country’s annual Golden Week holidays.