Study: Fewer Coronavirus Cases if Diamond Princess Had Been Evacuated

A new study indicates that while the quarantine measures aboard Diamond Princess reduced the number of passengers who caught coronavirus, the number would have been even lower if they had been allowed to disembark the ship. 

The study, published Friday in the Journal of Travel Medicine, compared the known transmission rates of the virus at its point of origin in Wuhan, China to the transmission rate aboard Diamond Princess. Using mathematical modeling, a team led by Prof. Joacim Rocklöv of Umeå University found that the initial rate aboard the cruise ship was found to be four times higher than that on land. If left unchecked throughout the period in which passengers were onboard - January 21 through February 19, the end of the quarantine period - roughly 2,920 out of the 3,700 people on board (about 80 percent) would likely have been infected. 

However, Japanese public health authorities took action, including isolating known cases on board and quarantining all passengers to their cabins beginning February 4. Thanks to these measures, only 619 cases were confirmed by February 20 (plus additional cases diagnosed after disembarkation). "Isolation and quarantine therefore prevented 2,307 cases," the authors wrote. 

However, if the passengers had been evacuated from the ship on February 3 - the date that the contagion was discovered on board - only about 76 people would have caught the virus, the team found. 

"The cruise ship conditions clearly amplified an already highly transmissible disease," the authors wrote. "The public health measures prevented more than 2000 additional cases compared to no interventions. However, evacuating all passengers and crew early on in the outbreak would have prevented many more passengers and crew from infection."