Cruise ships carrying COVID-19-vaccinated populations applied near-identical nonpharmaceutical measures during July-November 2021; passenger masking was not applied on 2 ships. Infection risk for masked passengers was 14.58 times lower than for unmasked passengers and 19.61 times lower than in the community. Unmasked passengers' risk was slightly lower than community risk.
Keywords: COVID-19; Europe; FFP2; N95; SARS-CoV-2; antibodies; coronavirus; cruise; facemask; investigation; isolation; mask; nonpharmaceutical measures; outbreak; physical distancing; quarantine; respiratory infections; sanitation; severe acute respiratory syndrome coronavirus 2; ship; surveillance; travel; vaccine; vessel; viruses; zoonoses.