Abstract: Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is in the pandemic.SARS-CoV-2 is believed to originate from natural evolution.This RNA virus keeps evolving, even during spillover into humans via intermediate hosts.The evolutionary trend of SARS-CoV-2 in humans is characterized as an increased human-to-human transmission.The current major countermeasures against COVID-19 pandemic remain to be public health interventions, specifically targeting to the transmission pathway.In addition, the key point for the prophylaxis is to screen and isolate asymptomatic SARS-CoV-2 carriers, which may be a crucial source of infection.The efficiency of active immunization using vaccine to protect susceptible population needs to be extensively evaluated in population of large scale.