Research on transmission pattern of SARS-CoV-2

  Objective  Taking the three outbreaks caused by Delta variant (B.1.617.2) in Guangzhou, Guangdong Province, Nanjing, Jiangsu Province and Zhengzhou, Henan Province as examples, to explore different transmission pattern of SARS-CoV-2 epidemic and to provide basis for scientific prevention and control.

  Methods  The research data was collected from the public data based on three related epidemics in Guangzhou, Nanjing and Zhengzhou reported by the national and local health commissions. Taking prefecture level city as the unit, according to the characteristics of infected cases movement, the epidemic transmission pattern was divided into jumping transmission and community transmission, and compared the two patterns of its characteristics.

  Results   From May 21 to September 3, 2021, 1 494 infected cases were reported in the three epidemics, including 83 cases of jumping transmission infections and 1 411 cases of community transmission infections including 884 infected cases caused by jumping transmission. Jumping transmission spread to a total of 45 cities for 22 days. The average age of the infected population was 37.15 years old, and the proportion of asymptomatic was 26.51%. The duration of community transmission was 65 days, and the average age of the infected population was 45.21 years old, the proportion of asymptomatic in which was 8.65%. The age of infected population was lower than that of jumping transmission, the proportion of asymptomatic was higher, and these differences were significant (P<0.001).

  Conclusion  The jumping transmission caused by population movement covered a wide range, with high proportion of young person and asymptomatic infected cases. Infections of community transmission were mainly middle-aged and elderly people. Therefore, it is suggested that differentiated control should be taken for different groups, such as strengthening the frequency of nucleic acid testing for mobile people and people in transportation hub, reducing gathering activities for community groups that reducing the frequency of contact can reduce the probability of infection.