Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2023

 The circulation of human influenza in the Oceanic region following the COVID-19 pandemic (#206)

Megan Triantafilou 1 , Heidi Peck 1 , Ian G Barr 1 2 , Sheena G Sullivan 1 3 4 , Tanya Diefenbach-Elstob 1
  1. WHO Collaborating Centre for Reference and Research on Influenza, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
  2. Department of Immunology and Microbiology, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
  3. Communicable Diseases, Health Protection Branch, Health Protection Branch, Public Health Division, Department of Health, Melbourne , Victoria, Australia
  4. Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Melbourne , Victoria, Australia

Background:

Influenza activity was historically low during 2020-2021 globally during the COVID-19 pandemic due to border closures, travel related quarantine, lockdowns and social distancing measures. After the after the reintroduction of international travel and cessation of non-pharmaceutical interventions, influenza outbreaks returned to pre-pandemic levels in much of Australia and Oceania in 2022 and have continued in 2023.

Methods:

We analysed virological data from influenza viruses sent to the WHO Collaborating Centre for Reference and Research on Influenza (WHOCC RRI), and also epidemiological surveillance data obtained from the WHO FluNet database and the Australian Influenza Surveillance Report (AISR) and the Australian NNDSS (National Notifiable Diseases Surveillance System). We examined trends in influenza numbers, types/subtypes, genomic characteristics and antiviral susceptibility from samples collected in Australia and the surrounding region in 2022-2023.

Results:

Influenza virus detections significantly increased in early 2022, beginning with large sustained outbreaks of influenza A(H3N2) in Darwin, Northern Territory, and in the Eastern States of Australia with the epidemic peaking in late June then quickly dissipating. The A(H3N2) subtype also caused outbreaks in many Oceanic countries such as Fiji and New Zealand in 2022. In 2023 outbreaks of influenza B (B/Victoria-lineage) occurred in Darwin and other Pacific Island nations such as Fiji, Tonga and Samoa. Unusually Fiji also experienced a large outbreak of A(H1N1) from December 2022-March 2023 along with a B/Victoria outbreaks from February-April 2023. New Caledonia also had A(H1N1)pdm09 and B/Victoria-lineage viruses circulating. A(H1N1) cases also increased in prevalence across Australia and New Zealand in 2023, along with B/Victoria cases with some A(H3N2) cases. No cases of influenza B Yamagata lineage have been detected worldwide since March 2020.

Conclusions:

After historically low levels of influenza during the COVID-19 Pandemic, 2022 saw influenza rebound to pre-pandemic levels in Australia, while many Pacific islands have seen continued outbreaks of influenza in 2022 and into 2023. The 2023 influenza season timing appears to be more typical in Australia-NZ to date with A(H1N1)pdm predominating in most of Oceania.