AISR fortnightly report no. 13 – 13 September to 26 September 2021
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The Australian Influenza Surveillance Report (AISR) is compiled from several data sources used to monitor influenza activity and severity in the community. These data sources include:
- laboratory-confirmed notifications to NNDSS
- influenza-associated hospitalisations
- sentinel influenza-like illness (ILI) reporting from general practitioners
- ILI-related community level surveys
- sentinel laboratory testing results.
The AISR is published fortnightly during the influenza season, typically between May and October. Influenza activity updates may be published outside of the seasonal period.
It is important to note that due to the COVID-19 epidemic in Australia, data reported from the various influenza surveillance systems may not represent an accurate reflection of influenza activity. Results should be interpreted with caution, especially where comparisons are made to previous influenza seasons. Interpretation of 2020 influenza activity data should take into account, but are not limited to, the impact of social distancing measures, likely changes in health seeking behaviour of the community including access to alternative streams of acute respiratory infection specific health services, and focussed testing for COVID-19 response activities. Current COVID-19 related public health measures and the community’s adherence to public health messages are also likely having an effect on transmission of acute respiratory infections, including influenza.
Following historically low activity levels observed from April 2020 onwards, community influenza-like-illness (ILI) activity in the year to date in 2021 remains at low levels.
Notifications of laboratory-confirmed influenza have also remained low since April 2020. In the year to date in 2021, there have been 534 notifications to the National Notifiable Diseases Surveillance System (NNDSS) in Australia, of which 21 notifications had a diagnosis date this fortnight.
There is no indication of the potential severity of the 2021 season at this time.
In the year to date, of the 534 notifications of laboratory-confirmed influenza, no influenza-associated deaths have been notified to the NNDSS.
There has been one hospital admission due to influenza reported across sentinel hospitals sites since commencement of surveillance in April 2021.
Given the low number of laboratory-confirmed influenza notifications, low community ILI activity, and low number of hospitalisations due to influenza at sentinel hospital sites, it is likely there is minimal impact on society due to influenza in 2021 to date.
In 2021 to date, adults aged 85 years and older, adults aged 60–69 years, children under 5 years of age, and adults aged 75–84 have the highest influenza notification rates.
To date, 68.2% of notifications of laboratory-confirmed influenza to the NNDSS were influenza A, of which 97.0% were influenza A (unsubtyped) and 3.0% were influenza A(H3N2). Influenza B accounted for 21.9% of notifications, 3.4% were influenza A and B co-infection, 0.4% were influenza C, and 6.2% were untyped.
Vaccine match and effectiveness
Of the 22 samples referred to the WHOCC to date, the 1 influenza B/Victoria sample and 1 influenza A(H1N1) sample were characterised as antigenically similar to the corresponding vaccine components, while the 20 influenza A(H3N2) samples were characterised as antigenically dissimilar.
The low case numbers of influenza across all systems in the season to date precludes meaningful analysis to estimate vaccine effectiveness for this season.