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SARS-CoV-2 Omicron variant BA.1 first emerged on the Chinese mainland on January 8, 2022, in Tianjin and caused a large wave of infections. 1 Four rounds of mass testing of its ~14 million residents were launched on January 9, 12, 15, and 20, respectively. As of February 7, 2022, a total of 430 individuals were tested positive for Omicron BA.1, with no new infections detected for the following 16 days.
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Zheng et al. (2022) studied this question.
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