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

We used data on confirmed cases on the cruise ship as published on a daily basis by public sources 17, 18 to calibrate a model and estimate the basic reproduction number from the time sequence and amplitude of the case rates observed. COVID-19 is thought to have been introduced by an index case from Hong Kong visiting the ship between the 21 st to 25 th of January, 2020. We thus used the date of 21 st January 2020 as the first time point, t=0, assuming the index case was infectious from the first day on the ship. The estimates of and the associated Covid-19 incidence on the cruise ship was derived using a compartmental model estimating the dynamics of the number of susceptible ( ), exposed ( ), infected ( ), and recovered ( ) individuals, adapted but modified from a published COVID-19 study. 19 We analyzed two instances of the model assuming respectively: (1) a homogenous population (3700 individuals), and (2) a stratified population of crew (1000 individuals) and guests (2700 individuals).