Coronavirus disease 2019 (COVID-19) is a novel human respiratory disease caused by the SARS-CoV-2 virus. Asymptomatic carriers of the virus display no clinical symptoms but are known to be contagious. Recent evidence reveals that this sub-population, as well as persons with mild and undocumented disease, represent a major contributor in the propagation of this disease. However, this method of transmission frequently escapes detection by public health surveillance systems. Because of this, the currently accepted estimates of the basic reproduction number (ℛ0) of the virus are inaccurate. Further, it is unlikely that a pathogen can blanket the planet in three months with an ℛ0 in the vicinity of 3, as reported (1–6). In this manuscript, we present a mathematical model taking into account asymptomatic and other undocumented carriers. Our results indicate that an initial value of the effective reproduction number could range from 5.5 to 26.5. Results from the first three weeks of the model exhibit exponential growth, which is in agreement with average case data collected from thirteen countries with universal health care and robust communicable disease surveillance systems; the average rate of growth in the number of reported cases is 23.3% per day during this period.
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