Objective  To explore epidemiological characteristics and re-positivity incidence of imported and local infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant during a period of coronavirus disease 2019 (COVID-19) epidemic in Fujian province.

  Methods  From National Information System of Disease Prevention and Control and Information System of Public Health Emergency Management, we extracted the information on 69 genome sequencing-confirmed imported infections and 264/212 genome sequencing-/epidemiologically confirmed local infections with SARS-CoV-2 Delta variant registered in Fujian province from March 2021 through February 2022. Descriptive statistics was used to analyze disease characteristics and incubation period of the SARS-CoV-2 Delta variant infections. The 'R0' and 'EpiEstim' packages of R software were used to estimate the serial interval (SI) and the time-dependent reproduction number (Rt). Influencing factors of the re-positivity were analyzed with logistic regression.

  Results  The period of COVID-19 epidemic induced by SARS-CoV-2 Delta variant was approximately from March 2021 to February 2022 in Fujian province, with a continuous incidence of sporadic imported cases and local outbreak of the infections. The majority of the imported cases were seafarers (28.99%), students (15.94%) and commercial service personnel (14.49%) from Southeast Asia, Japan, the United States, the United Kingdom and other regions and entered Fujian province via Xiamen Customs. The local epidemics due to rapid transmission of Delta variant occurred mainly in schools and factories in Putian and Xiamen city. The SI of the local infections was fitted to Gamma distribution, with the mean and standard deviation of 2.28 and 2.06, respectively. For the 149 infector-infectee pairs of local infections during the local outbreak, the maximum value of Rt was 7.35 and the median incubation period was 6.50 days. The incidence of re-positivity was 37.98% for all the Delta variant infections. The results of multivariate regression analysis revealed that the local infections with Delta variant were at a significantly higher risk of re-positivity ( odds ratio = 2.47, 95% confidence interval: 1.25 – 4.87) compared to the imported infections. No associates of gender, age, occupation and clinical type with the re-positivity were observed.

  Conclusion  The period of COVID-19 epidemic due to SARS-CoV-2 Delta variant infections in Fujian province was approximately from March 2021 to February 2022, with continuously sporadic imported and local infections and the local epidemic was under effective control rapidly. The incidence rate of re-positivity was 37.98% among all infections with Delta variant.