Large gatherings of people on cruise ships and warships are often accompanied by an increase in the risk of COVID-19 infections. To assess the transmissibility of SARSCoV- 2 on warships and cruise ships and to quantify the effectiveness of containment measures. The transmission coefficient (β), basic reproductive number (R0), and time to deploy containment measures were estimated by the Bayesian Susceptible- Exposed-Infected-Recovered model. A meta-analysis was conducted to predict vaccine protection with or without non-pharmaceutical interventions. NPIs during the voyage could reduce the transmission coefficients of SARS-CoV-2 by 50% estimated from the meta-analyses. Two weeks into the voyage of a cruise that begins with 1 infected passenger out of 3711, we estimate there would be 45 (95% CI:25-71), 33 (95% CI:20-52), 18 (95% CI:11-26), 9 (95% CI:6-12), 4 (95% CI:3-5), and 2 (95% CI:2-2) final cases under 0%, 10%, 30%, 50%, 70% and 90% vaccines protection without NPIs, respectively. Timeliness of strict NPIs accompanied by quarantine and isolation is imperative when COVID-19 cases are introduced into cruise ships. The spread of COVID-19 on ships was predicted to be limited in scenarios corresponding to at least 70% protection from prior vaccination across all passengers and crew.
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