AISR – 2022 national influenza season summary

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 April and October. Influenza activity updates may be published outside of the seasonal period.

Key messages

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 influenza data from April 2020 onwards 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.

Reporting Period: 01 January – 09 October 2022

Activity

• The 2022 influenza season began earlier compared to recent years. While influenza and influenza-like illness (ILI) activity levels were higher than average across all systems, it was a shorter season with a large peak of laboratory-confirmed influenza notifications in early June. Notifications substantially decreased in July and remained low until the end of the 2022 season.

Severity

• The clinical severity for the 2022 influenza season was considered low. In the reporting period, of the 225,332 notifications of laboratory-confirmed influenza, 308 influenza-associated deaths (0.14%) were notified to the National Notifiable Disease Surveillance System (NNDSS).

Impact

• Given the high level of influenza activity in the community, it is likely there was low to moderate impact on society during the reporting period.

At-risk populations

• Children aged 5–9 years had the highest influenza notification rates during the reporting period, followed by children younger than 5 years. The notification rate was lowest among adults aged 70–74 years. 
• Of the 1,832 patients with confirmed influenza admitted to sentinel hospitals, 55.8% were children aged younger than 16 years, 24.3% were adults aged 16 to 64 years, and 19.9% were adults aged 65 years or older.

Virology

• During the reporting period, the majority of nationally reported laboratory-confirmed influenza cases were influenza A (82.7%). Influenza B accounted for 0.2% of notifications, less than 0.1% were influenza A and B co-infections, and 17.1% were untyped.

Vaccine effectiveness

• Based on preliminary data, the 2022 influenza vaccine significantly reduced the risk of hospitalisation with influenza. Estimated vaccine effectiveness was 44% (95% CI: 22%–60%).