[1] Feng YN, Zhao X, Chen ZX, Nie K, Yin ZY, Xia Y, et al. Genomic surveillance for SARS-CoV-2 variants of concern from imported COVID-19 cases — the mainland of China, 2021. China CDC Wkly 2022;4(31):680 − 4. http://dx.doi.org/10.46234/ccdcw2022.144CrossRef
[2] Chen C, Feng YN, Chen ZX, Xia Y, Zhao X, Wang J, et al. SARS-CoV-2 cold-chain transmission: characteristics, risks, and strategies. J Med Virol 2022;94(8):3540 − 7. http://dx.doi.org/10.1002/jmv.27750CrossRef
[3] Zhou L, Nie K, Zhao HT, Zhao X, Ye BX, Wang J, et al. Eleven COVID-19 outbreaks with local transmissions caused by the imported SARS-CoV-2 delta VOC — China, July–August, 2021. China CDC Wkly 2021;3(41):863 − 8. http://dx.doi.org/10.46234/ccdcw2021.213CrossRef
[4] World Health Organization. Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern. https://www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars-cov-2-variant-of-concern. [2022-8-13].https://www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars-cov-2-variant-of-concern
[5] Shuai HP, Chan JFW, Hu BJ, Chai Y, Yuen TTT, Yin FF, et al. Attenuated replication and pathogenicity of SARS-CoV-2 B. 1.1.529 Omicron. Nature 2022;603(7902):693 − 9. http://dx.doi.org/10.1038/s41586-022-04442-5CrossRef
[6] World Health Organization. Weekly epidemiological update on COVID-19 - 1 February 2023. https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---1-february-2023. [2023-2-1].https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---1-february-2023