ABSTRACT
BACKGROUND The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has affected the maritime sector due to virus transmission onboard and traffic restrictions. However, reports of SARS-CoV-2 transmission on board have been mostly restricted to those occurring on cruise ships. OBJECTIVES To report COVID-19 outbreaks in eight non-cruise vessels and discuss measures to prevent and control the onboard transmission of SARS-CoV-2. METHODS We investigated outbreaks of COVID-19 on vessels anchoring in Baía de Todos-os-Santos, Salvador, Brazil, between February and November 2021. FINDINGS Most vessels were cargo ships that had docked several times before anchoring in Salvador (five had docked in ≥ 9 ports). The crew ranged from 22 to 63 members. The infection attack rate on each vessel ranged from 9.7 to 88.9%. The risk of symptomatic infection largely varied among the crew of each vessel (0 to 91.6%). Overall, the risk of developing COVID-19 signs and symptoms was lower among crew members vaccinated (age-adjusted risk ratio: 0.19; 95% confidence interval 0.06-0.65). SARS-CoV-2 variants not previously identified in Salvador were detected (C.14, B.1.617.2 and B.1.351). MAIN CONCLUSIONS Despite maritime guidelines to avert COVID-19 on board, outbreaks have happened. The multiple stopovers of non-cruise vessels during their routes may contribute to the spread of SARS-CoV-2 variants worldwide. Reducing the onboard transmission of SARS-CoV-2 depends on joint efforts by the crew and local health authorities and, equally important, achieving high vaccination coverage to prevent infections and illness.