The horizontal dashed line shows Rt at 1.0. The vertical dashed line shows when quarantine was implemented (Feb. 5, 2020). 

Smith College

In (Tokyo) Japan, most infections of COVID-19 have been linked back to a party in a traditional wooden ship, called a Yakatabune. In Yokohama, Japan, there has been another outbreak on board the Princess Cruise Ship. After the two week quarantine period came to an end, 621 people on board the ship tested positive for COVID-19, out of the total 3,711 passengers and crew members on board. The effective reproduction number (Rt) had a maximum value of 11.2 (the epidemic threshold is 1.0). In this instance, it was found that passenger to passenger transmission type dominated. The Japanese government handled this outbreak well, and have kept the confirmed number of COVID-19 cases below 20,000 as of July 6, 2020. 

Transmission Potential of COVID-19 in Japan

Mizumoto, K., &amp; Chowell, G. (2020). Transmission potential of the novel coronavirus (COVID-19) onboard the diamond Princess Cruises Ship, 2020. Infectious Disease Modelling, 5, 264-270. doi:10.1016/j.idm.2020.02.003
https://www.sciencedirect.com/science/article/pii/S2468042720300063

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