[1] Tan ZL, Chen ZX, Yu AP, Li XY, Feng YN, Zhao X, et al. The first two imported cases of SARS-CoV-2 omicron variant-Tianjin municipality, China, December 13, 2021. China CDC Wkly 2022;4(4):76 − 7. http://dx.doi.org/10.46234/ccdcw2021.266CrossRef
[2] Yang W, Shaman J. SARS-CoV-2 transmission dynamics in South Africa and epidemiological characteristics of the Omicron variant. medRxiv 2021. http://dx.doi.org/10.1101/2021.12.19.21268073.http://dx.doi.org/10.1101/2021.12.19.21268073
[3] Ma HL, Wang ZG, Zhao X, et al. Long distance transmission of SARS-CoV-2 from contaminated cold chain products to humans-Qingdao city, Shandong Province, China, September 2020. China CDC Wkly 2021;3(30):637 − 44. http://dx.doi.org/10.46234/ccdcw2021.164CrossRef