Detection of Influenza in Managed Quarantine in Australia and the Estimated Risk of Importation.

BACKGROUND

Influenza circulated at historically low levels during 2020/2021 due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic travel restrictions. In Australia, international arrivals were required to undergo a 14-day hotel quarantine to limit new introduction of SARS-CoV-2.

METHODS

We usedtesting data for travelers arriving on repatriation flights to Darwin, Australia, from 3 January 2021 to 11 October 2021 to identify importations of influenza virus into Australia. We 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 were used to infer the risk of influenza cases exiting quarantine while infectious.

RESULTS

Despite very low circulation of influenza globally, 42 cases were identified among 15 026 returned travelers, of which 30 were A(H3N2), 2 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 travelers 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. Failure to test quarantined returned travelers for influenza represents a missed opportunity for enhanced surveillance to better inform public health preparedness.

Informations de copyright

© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: [e-mail].

Déclaration de conflit d'intérêts

Potential conflicts of interest. B. J. C. reports consulting fees paid to author from AstraZeneca, Fosun Pharma, GSK, Moderna, Pfizer, Roche, and Sanofi Pasteur. S. G. S. reports OptumLabs research credits through the University of California (no funding received; had access to data for 1 year) to study the influenza infection and vaccination outcomes during pregnancy; participated in advisory boards for influenza vaccines for Seqiris and Sanofi (no remuneration received); from 2017–2021, served as a member of the WHO Strategic Advisory Group of Experts on Immunization Working Group on Influenza (unpaid); since 2011, has been an observer or invited member of the National Influenza Surveillance Committee for the Australian Government (unpaid); WHO Collaborating Centre for Reference and Research on Influenza [employer] receives funding from the International Federation of Pharmaceutical Manufacturers & Associations (IFPMA) for the development of influenza vaccines and CSL Seqirus. All remaining authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.