London, Feb 29 The over two-week-long quarantine on cruise ship Diamond Princess resulted in more passengers getting infected by the virus than if they would have disembarked immediately, says a study.
"The infection rate onboard the vessel was about four times higher than what can be seen on land in the worst infected areas of China. A probable cause is how close people stay to one another onboard a vessel," said principal author Joacim Rocklov, Professor of Epidemiology at Umea University in Sweden.
After a person travelling with the cruise ship Diamond Princess disembarked in Hong Kong and was tested positive for the coronavirus, Japanese authorities decided to disallow the 3,700 passengers onboard to leave the ship when it reached Yokohama.
The ship was hence put in quarantine until February 19. Passengers who showed signs of illness were, as far as possible, separated from other passengers onboard.
When the quarantine in Yokohama in the end was removed and passengers could finally disembark, a total of 619 of 3,700 passengers and crew were tested positive.
The number of infected passengers subsequently rose to over 700. At least six of them have died.
"If the ship had been immediately evacuated upon arrival in Yokohama, and the passengers who tested positive for the coronavirus and potential others in the risk zone had been taken care of, the scenario would have looked quite different," Rocklov said.
"Our calculations show that only around 70 passengers would have been infected. A number that greatly falls short of the over 600 passengers the quarantine resulted in," Rocklov said.
"The precautionary measure of putting the entire ship under quarantine was understandable, but due to the high risk of transmission on the ship, the decision is now questionable," he added.
For the study, published in the Journal of Travel Medicine, the researchers estimated the basic reproduction number from the initial period of the outbreak using SEIR models which assume people carry lifelong immunity to a disease upon recovery.
The researchers also compared scenarios of an earlier versus later evacuation of the ship.
At the same time, the study also showed that if the precautionary measures of isolating potential carriers had not been carried out onboard, another 2,300 people would have been infected.
Formally established in 1965, Umea University covers research and education in medicine, science and technology, social sciences, arts and humanities, and educational sciences.
( With inputs from IANS )