Contrasting SARS-CoV-2 epidemics in Singapore: Cohort studies in migrant workers and the general population

Abstract From January 2020, Singapore implemented comprehensive measures to suppress SARS-CoV-2. Community transmission has been limited, although explosive outbreaks have occurred in migrant worker dormitories. We conducted longitudinal SARS-CoV-2 serology studies among 478 residents of a SARS-CoV-2 affected migrant worker dormitory between May and July 2020, and 937 community-dwelling adult Singapore residents with sera collected before September 2019 and in November/December 2020. By end 2020, <2 per 1000 (0.16%, 95% CrI: 0.008% - 0.72%) adult residents in the community were infected with SARS-CoV-2, approximately 4 times higher than the national notified case incidence. In contrast, in the migrant worker cohort, nearly two-thirds 63.8% (95% CrI: 57.9% - 70.3%) had been infected by July 2020; no symptoms were reported in >90% of these infections. SARS-CoV-2 suppression is feasible with rapid implementation of comprehensive control measures. However, the risk of large-scale epidemics in densely-populated environments requires specific consideration in preparedness planning.