Background Influenza circulated at historically-low levels during 2020 and 2021 due to COVID-19 pandemic travel restrictions. In Australia, international arrivals to Australia were required to undertake 14 days hotel quarantine to limit new introduction of SARS-CoV-2 virus. Methods We used routine testing data for travellers arriving on repatriation flights to Darwin, Australia from 3 January to 11 October 2021 to identify importations of influenza virus into Australia and used this information to estimate the risk of a case exiting quarantine while still infectious. Influenza-positive samples were sequenced and cases were followed-up to identify transmission clusters. Data on the number of cases and total passengers was used to infer the risk of influenza cases existing quarantine while infectious. Results Despite very low circulation of influenza globally, 42 cases were identified among 15,026 returned travellers, of which 30 were A(H3N2), two were A(H1N1)pdm09 and 10 were B/Victoria. Virus sequencing data identified potential in-flight transmission, as well as independent infections prior to travel. Under the quarantine strategy in place at the time, the probability that these cases could initiate influenza outbreaks in Australia neared 0. However, this probability rose as quarantine requirements relaxed. Conclusions Detection of influenza virus infections in repatriated travellers provided a source of influenza viruses otherwise unavailable and enabled development of the A(H3N2) vaccine seed viruses included in the 2022 Southern Hemisphere influenza vaccine. Failing to test quarantined returned travellers for influenza, represents a missed opportunity for enhanced surveillance to better inform public health preparedness.

中文翻译：

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澳大利亚管理检疫中流感的检测和输入风险的估计

背景 由于 COVID-19 大流行病旅行限制，2020 年和 2021 年期间流感的传播处于历史低位。在澳大利亚，抵达澳大利亚的国际旅客必须进行 14 天的酒店隔离，以限制 SARS-CoV-2 病毒的新传入。方法 我们使用了 2021 年 1 月 3 日至 10 月 11 日期间搭乘遣返航班抵达澳大利亚达尔文的旅客的常规检测数据，以确定流感病毒输入澳大利亚的情况，并使用该信息来估计病例在仍具有传染性的情况下退出隔离区的风险。对流感阳性样本进行了测序，并对病例进行了随访，以确定传播簇。病例数和乘客总数的数据被用来推断流感病例在具有传染性的情况下存在检疫的风险。结果 尽管全球流感流行率很低，但在 15,026 名回国旅客中发现了 42 例，其中 30 例为 A(H3N2)，2 例为 A(H1N1)pdm09，10 例为 B/Victoria。病毒测序数据确定了潜在的飞行中传播，以及旅行前的独立感染。在当时实施的隔离策略下，这些病例在澳大利亚引发流感爆发的可能性接近于 0。然而，随着隔离要求的放松，这一可能性有所上升。结论 在遣返旅行者中检测到流感病毒感染提供了流感病毒的来源，否则无法获得该来源，并使 2022 年南半球流感疫苗中包含的 A(H3N2) 疫苗种子病毒得以开发。未能对隔离的返回旅客进行流感检测，