The Diamond Princess is a British-registered luxury cruise ship that is operated by Princess Cruises, a holiday company based in the United States and Bermuda. In February 2020, during a cruise of the Western Pacific, cases of COVID-19 were detected on board. The vessel was quarantined off Japan for two weeks, after which all remaining passengers and crew were evacuated. Of the 3,711 people on board, 712 became infected with the virus – 567 of 2,666 passengers, and 145 of 1,045 crew. Figures for total deaths vary from early to later assessments, and because of difficulties in establishing causation. As many as 14 are reported to have died from the virus, all of them older passengers – an overall mortality rate for those infected of 2%.
Timeline
The Diamond Princess departed from the Port of Yokohama on 20 January 2020 for a round-trip billed as a tour of Southeast Asia during the Lunar New Year period, with 2,666 passengers and 1,045 crew on board.
An 80-year-old passenger from Hong Kong had embarked in Yokohama on 20 January. He had been in Shenzhen, Guangdong Province, China on 10 January, then returned to Hong Kong and flew to Tokyo on 17 January to board the ship. He developed a cough on 19 January, but he went on board. He left the cruise when the ship reached Hong Kong on 25 January.
The cruise continued. On 31 January, the ship docked in Taiwan, which according to Vice Premier Chen Chi-mai was "the earliest country to activate epidemic prevention measures against this disease". A paper in the Journal of Medical Internet Research authored by Chen, describes how the passengers of the COVID-19 stricken cruise ship were later traced using mobile phone geolocation, and how their 627,386 contacts were alerted through text messaging.
On 1 February, the ship called at Naha Port in Okinawa and was quarantined. On the same day, the 80-year-old man who disembarked in Hong Kong six days earlier tested positive for COVID-19. Having a fever, he went to the hospital and got tested.
Hong Kong's Department of Health immediately contacted the agent of the ship's operating company, but the ship did not inform the passengers until 3 February, two days later.
Over the next few days, the cruise ship had shows and dance parties as usual and also continued to open public facilities that attract large crowds, including fitness clubs, theatres, casinos, bars, and buffet-style restaurants.
On the evening of 3 February, the cruise ship returned to Yokohama Port and anchored off the coast of Daikoku Pier without docking.
The Japanese government decided to re-quarantine the ship. Officials of the Ministry of Health, Labour and Welfare boarded the ship for quarantine.
On 4 February, tests revealed infections of 10 out of 31 people tested. The authorities immediately decided to isolate all passengers on board for 14 days. On 5 February, the authorities announced positive test results for SARS-CoV-2 for 10 people on board, the cancellation of the cruise, and that the ship was entering quarantine for 14 days based on World Health Organization guidelines.
A total of 3,700 passengers and crew were quarantined by the Japanese Ministry of Health, Labour and Welfare for what was expected to be a 14-day period, off Yokohama.
On 7 February, the total number of people on board with confirmed SARS-CoV-2 infections grew to 61.
Another three cases were detected on 8 February, bringing the total to 64.
On 9 February, six cases were detected, while another 65 were detected on 10 February, bringing the total to 135.
The numbers overwhelmed local medical facilities, and stricken passengers were divided into three groups according to condition, and evacuated to suitable locations, allowing intensive care to perform as intended.
On 11 February, 39 more people tested positive for the virus, including one quarantine officer, bringing the total to 174.
Passengers with confirmed cases were reported to be taken ashore for treatment.
On 13 February, 44 more people tested positive for the virus, bringing the total to 218.
On 15 February 67 more people were reported to be infected, bringing the total to 285.
On 16 February 70 more people were reported to be infected, bringing the total to 355.
The next day on 17 February, the Ministry of Health, Labour and Welfare confirmed 99 more cases, raising the total to 454, 33 of whom were crew members.
On 18 February, another 88 cases were confirmed, bringing the total to 542.
On the morning of 17 February (Japan time), two U.S. government-chartered planes departed for the United States, carrying hundreds of U.S. citizens who were passengers of the cruise ship. Among about 400 American passengers, 328 boarded the planes, excluding those who expressed their intention to stay on the ship and 44 under treatment in Japan.
The U.S. government initially asked Japan to keep them on board for 14 days based on the CDC guideline despite the proposal by the Japanese government to bring American passengers back home early.
The U.S. government, however, changed its policy to return home on 15 February.
The first plane landed at Travis Air Force Base in California at midnight on 16 February (U.S. time), and the other plane landed at Joint Base San Antonio in Texas on the early morning of 17th (U.S. time).
Canada, Hong Kong, Australia and Italy also followed the United States within a few days. There were 164 Australian passengers, of whom 24 were infected, and all Australian passengers were sent for 14 days quarantine to Darwin.
On 18 February, Michael J. Ryan, executive director of the World Health Organization's Health Emergencies Programme, said that Japan's measures to quarantine passengers and staff on board at the Yokohama Port for two weeks were preferable to having them scattered throughout the world. However, he said that he was disappointed at the continued increase in the number of infected people.
On 18 February, Kentaro Iwata, an infectious disease expert at Kobe University, uploaded a video on YouTube in which he raised questions about the measures taken to prevent epidemics on Diamond Princess shortly after boarding the ship. He removed it on 20 February.
On 19 February, passengers with negative test results began to disembark.
On 20 February, the World Health Organization's Director-General reported the total number of the cases outside of China to be 1,076, and stated that over half of these cases occurred among the passengers on the Diamond Princess.
By late March, it was stated that 712 of 3,711 people on the Diamond Princess, or 19.2%, had been infected by COVID-19.
By 1 March, all passengers and crew members had disembarked from the ship.
In early March 2020, Indonesia evacuated 69 Indonesian crew of Diamond Princess, after their COVID-19 test results in Japan were negative. However, an Indonesian naval hospital ship bringing them to Sebaru Island for a mandatory quarantine period had two crew ill. All were tested again; 67 passed the second test, but two did not and were retested with a more accurate, different test, with one negative and one positive result. The 68 people with negative tests disembarked at Sebaru Island for observation and the one positive case was evacuated by helicopter to Persahabatan Hospital.
Eventually, all 69 crew members received negative COVID-19 test results.
On 16 May, Diamond Princess departed from the Port of Yokohama and began sailing to Port Dickson, Malaysia.
Criticism
There are many criticisms of Japan's epidemic prevention measures of quarantine on cruise ships.
There is the possibility that quarantine in a cruise ship is dangerous, because a cruise ship does not use HEPA filters which can effectively screen 99 percent of the particles, as is used in modern aircraft.
Kentaro Iwata, an infectious diseases expert at Kobe University who visited the ship, strongly criticised the management of the situation in two widely circulated YouTube videos published on 18 February. He called Diamond Princess a "COVID-19 mill".
He said that the areas possibly contaminated by the virus were not in any way separated from virus-free areas, there were numerous lapses in infection control measures, and that there was no professional in charge of infection prevention – the bureaucrats were in charge of everything.
Japanese officials denied the accusations and argued that the zoning on board, of course, was not perfect, but it was not insane from the medical point of view.
Yoshihiro Yamahata and Ayako Shibata, two medical doctors who attended to the passengers as first responders, wrote later that "at the beginning of implementation of the quarantine, we had to enact measures based on limited information, which is confusing" and that "it was thought that COVID-19 could not be spread via human-to-human transmission", which explains why there "might be a gap between the new and old infection control measures". While the U.S. Centers for Disease Control and Prevention commended the efforts to institute quarantine measures, their assessment was that it may have not been sufficient to prevent transmission among people on the ship.
Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said that the quarantine process had failed.
Dr. Yoshihiro Takayama, who worked on Diamond Princess as a member of the Ministry of Health, Labor and Welfare and helped Iwata get on board as a nominal member of DMAT, pointed out and corrected Iwata's errors on Facebook, saying the video could put ship passengers, crew, and medical staff in a corner.
Takayama also revealed that Iwata was forced to leave the ship in two hours and only looked around the lounge, and he had been dismissed due to trouble with DMAT members and staff.
The authorities also admitted at a press conference that Iwata, who was a member of the DMAT, tried to act alone, so they asked him to leave.
The next day on 20 February, Iwata removed his videos and apologised to those involved, but still insisted the situation on the ship had been chaotic.
A preliminary report based on the first 184 cases by Japan's National Institute of Infectious Diseases (NIID) estimated that most of the transmission on the ship had occurred before the quarantine.
The cruise line, Princess Cruises, had first assumed there was only minimal risk and had initiated only the lowest-level protocols for outbreaks before the quarantine.
By 27 February, at least 150 of the crew members had tested positive for the virus.
Dr. Norio Ohmagari, top government adviser and director of Japan's Disease Control and Prevention Center admitted that the quarantine process might not have been perfect. A crew member reported that many of the crew had been expected to still work and interact with passengers even under the quarantine.
Princess Cruises stated that Japan's ministry of health was the lead authority defining and executing quarantine protocols, yet Japan's ministry of foreign affairs stated that a criterion of behavior was presented but the ultimate responsibility for safe environment rested with the ship operator.
Food service workers were found to have likely been the main early route of spread.
46.5% of the infected passengers and crew members had no symptoms at the time of testing.
The ship outbreak had a basic reproduction number of 14.8; much higher than the usual 2–4.
Calculations indicate that an early evacuation could have reduced the case number to just 76 cases, and that the applied quarantine reduced the case number by about 2300 cases.
Survey report
Professor Hiroshi Nishiura of Hokkaido University, a member of Novel Coronavirus Expert Meeting, analyzed the days when they were infected based on the data of the onset date and incubation period of passengers and crews. It was speculated that passengers were infected during the three days from February 2 to 4.
However, the crew, who continued to support the lives of passengers as "essential workers", became infected a week after the cruise ship anchored.
Although strict rules were laid out and medical equipment such as N95 masks were distributed to them, it was difficult for those who were not medical workers to act as instructed.
The living environment of their communal living also increased the risk.
There was no bias or regularity in the distribution of infected sites on the cruise ship.
After searching for traces of the virus's genes, the most common place was modular bathroom floors.