The first three months of the COVID-19 epidemic: Epidemiological evidence for two separate strains of SARS-CoV-2 viruses spreading and implications for prevention strategies

About one month after the COVID-19 epidemic peaked in Mainland China and SARS-CoV-2 migrated from China westward to Europe and then the U.S., the epidemiological data begin to provide important insights into the risks associated with the disease and the effectiveness of intervention strategies. Like other respiratory diseases, including the 2003 SARS epidemic, the virus remains only about two months in any given population, yet the peak incidence and the lethality can vary. The data suggest that at least two strains of the 2020 SARS-CoV-2 virus have evolved during its migration from Mainland China to Europe. South Korea, Iran, and Italy were hit by the more dangerous "SKII" variant. While the epidemic in China is about to end, and in Europe about to level off, the course of the epidemic in the younger US population is still increasing and the peak level will likely depend on which of the strains has entered the US first.