COVID-19 outbreak on the Diamond Princess cruise ship: estimating the epidemic potential and effectiveness of public health countermeasures

Rocklöv, J; Sjödin, H; Wilder-Smith, A

where the infectious period equals to one over the recovery rate ( ), In the homogeneous model, the infectious period, i, of COVID-19 was set to be 10 days based on previous findings. 8 In the situation of no removal (ill persons taken off the ship to be isolated in a Japanese hospital), the incubation period (or, the latent period), was estimated to be approximately 5 days (ranging from 2 to 14 days). 20 In order to model the removal/isolation and quarantine interventions, we implemented time dependent removal and contact rates as described in Table 1 . We performed additional sensitivity analysis reducing the to 3.7, an estimate of the average value across mainland China studies of COVID-19. 9 We further estimated a counterfactual scenario of the infections dynamics assuming no interventions were implemented, in particular no removal and subsequent isolation of ill persons. We assumed an infectious period of 10 days, with a contact rate remaining the same as in the initial phase of the outbreak. Additionally, in the stratified model of crew and guests, the contact rate was assumed to be different due to the assumption that crew could not be easily quarantined as they had to continue their services on board for all the passengers and possibly had more homogeneous mixing with all the passengers, whereas passengers may be mixing more within their preferred circles and areas. We kept the transient change in the contact rate and the removal of all PCR confirmed patients starting from the 3 nd and the 5 th of February respectively as in the first model. Parameters are described in Table 1 .