Understanding the outbreak dynamics of the COVID-19 pandemic has important implications for successful containment and mitigation strategies. Recent studies suggest that the population prevalence SERO of SARS-CoV-2 antibodies SERO, a proxy for the number of asymptomatic TRANS cases, could be an order of magnitude larger than expected from the number of reported symptomatic cases. Knowing the precise prevalence SERO and contagiousness of asymptomatic TRANS transmission TRANS is critical to estimate the overall dimension and pandemic potential of COVID-19. However, at this stage, the effect of the asymptomatic TRANS population, its size, and its outbreak dynamics remain largely unknown. Here we use reported symptomatic case data in conjunction with antibody SERO seroprevalence SERO studies, a mathematical epidemiology model, and a Bayesian framework to infer the epidemiological characteristics of COVID-19. Our model computes, in real time, the time-varying contact rate of the outbreak, and projects the temporal evolution and credible intervals of the effective reproduction number TRANS and the symptomatic, asymptomatic TRANS, and recovered populations. Our study quantifies the sensitivity SERO of the outbreak dynamics of COVID-19 to three parameters: the effective reproduction number TRANS, the ratio between the symptomatic and asymptomatic TRANS populations, and the infectious periods TRANS of both groups For nine distinct locations, our model estimates the fraction of the population that has been infected and recovered by Jun 15, 2020 to 24.15% (95% CI: 20.48%-28.14%) for Heinsberg (NRW, Germany), 2.40% (95% CI: 2.09%-2.76%) for Ada County (ID, USA), 46.19% (95% CI: 45.81%-46.60%) for New York City (NY, USA), 11.26% (95% CI: 7.21%-16.03%) for Santa Clara County (CA, USA), 3.09% (95% CI: 2.27%-4.03%) for Denmark, 12.35% (95% CI: 10.03%-15.18%) for Geneva Canton (Switzerland), 5.24% (95% CI: 4.84%-5.70%) for the Netherlands, 1.53% (95% CI: 0.76%-2.62%) for Rio Grande do Sul (Brazil), and 5.32% (95% CI: 4.77%-5.93%) for Belgium. Our method traces TRANS the initial outbreak date in Santa Clara County back to January 20, 2020 (95% CI: December 29, 2019 - February 13, 2020). Our results could significantly change our understanding and management of the COVID-19 pandemic: A large asymptomatic TRANS population will make isolation, containment, and tracing TRANS of individual cases challenging. Instead, managing community transmission TRANS through increasing population awareness, promoting physical distancing, and encouraging behavioral changes could become more relevant.