The Delta variant strain is one of the most prevalent variant subtypes of New Coronavirus in the world, characterized by rapid transmission, high infectivity, and atypical initial symptoms. At the same time, it may increase the severity of New Coronavirus pneumonia and weaken the protective effect of the vaccine, which is a particularly problematic issue in various countries. However, current vaccine data in China show that vaccination can effectively reduce its transmission capacity as well as the rate of weight transfer, which means that the current vaccine still has a good preventive as well as protective effect on it. The transmission index of the Delta mutant strain has increased by 100% compared to other older strains, which is equivalent to a doubling. At the same time, the speed of transmission has been significantly reduced, as evidenced by the shortening of the incubation period and the transmission interval, and even the phenomenon of “14-second transmission”. Without vaccine immunization and strong and effective control measures, the multiplication rate of the epidemic would have been significant. In addition, compared to the previous New Coronavirus, the Delta variant may show atypical symptoms in the early stages of infection, which may simply be malaise, or impaired sense of smell, or mild muscle aches. This results in a more insidious onset and does not facilitate detection and control of the disease. Therefore, daily personal protection is still needed. Studies have shown that the Delta mutant strain may have a stronger rate of reassortment than before. However, due to the current high vaccination rate in China, the rate of reassortment of the delta variant is still low and is mainly related to the underlying disease of the patient. And because of the large amount of clinical experience already available, most patients with mild disease now have a good prognosis. In order to better prevent and control the outbreak, timely vaccination is recommended, while it is still necessary to wear masks, wash hands frequently, gather less often and pay attention to one’s health on a daily basis.