Estimating relative generation times and reproduction numbers of Omicron BA.1 and BA.2 with respect to Delta variant in Denmark
Estimating relative generation times and reproduction numbers of Omicron BA.1 and BA.2 with respect to Delta variant in Denmark
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DOI：
10.3934/mbe.2022418
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发表时间：
2022-01-01
影响因子：
2.6
通讯作者：
Nishiura, Hiroshi
中科院分区：
文献类型：
--
作者：
Ito, Kimihito;Piantham, Chayada;Nishiura, Hiroshi
Omicron变异体在严重急性呼吸系统综合征冠状病毒2（SARS-CoV-2）中传播最快。Omicron的BA.1和BA.2亚系在世界范围内流行，迫切需要评估这些亚系的传播优势。使用描述变异频率轨迹的数学模型，假设变异体之间的平均世代时间的恒定比率和有效繁殖数的恒定比率，分析了丹麦2021年11月22日至2022年2月26日的变异频率轨迹。在当时的流行条件下，Omicron BA.1的平均世代时间是Delta的0.44-0.46倍，有效繁殖数是Delta的1.88-2.19倍。Omicron BA.2的平均世代时间是BA.1的0.76-0.80倍，有效繁殖数是BA.1的1.25-1.27倍。这些估计的比例的平均世代时间和有效繁殖数量的比例有流行病学上的重要意义。Omicron BA.2感染的接触者追踪必须比BA.1更快地进行，以通过隔离来阻止进一步的感染。在丹麦人群中，与BA.1相比，针对Omicron BA.2的控制措施需要减少20-21%的额外接触。
The Omicron variant spreads fastest as ever among the severe acute respiratory syndrome coronaviruses 2 (SARS-CoV-2) we had so far. The BA.1 and BA.2 sublineages of Omicron are circulating worldwide and it is urgent to evaluate the transmission advantages of these sublineages. Using a mathematical model describing trajectories of variant frequencies that assumes a constant ratio in mean generation times and a constant ratio in effective reproduction numbers among variants, trajectories of variant frequencies in Denmark from November 22, 2021 to February 26, 2022 were analyzed. We found that the mean generation time of Omicron BA.1 is 0.44-0.46 times that of Delta and the effective reproduction number of Omicron BA.1 is 1.88-2.19 times larger than Delta under the epidemiological conditions at the time. We also found that the mean generation time of Omicron BA.2 is 0.76-0.80 times that of BA.1 and the effective reproduction number of Omicron BA.2 is 1.25-1.27 times larger than Omicron BA.1. These estimates on the ratio of mean generation times and the ratio of effective reproduction numbers have epidemiologically important implications. The contact tracing for Omicron BA.2 infections must be done more quickly than that for BA.1 to stop further infections by quarantine. In the Danish population, the control measures against Omicron BA.2 need to reduce 20-21% of additional contacts compared to that against BA.1.