Are we on the brink of big flu numbers?

3 minute read

This time last year cases were about to explode. Are we about to get hit hard again?

If 2023’s flu season proceeds like 2022’s, we are days away from a precipitous rise in case numbers, despite early signs the outbreak may not reach the heights initially feared. 

The latest Australian Influenza Surveillance Report for weeks 16 and 17 is noncommittal when it comes to predicting severity, saying it is still too early to tell. 

This time last year, however, the numbers were similarly small but exploded in weeks 18 through 25, suggesting we could be on the brink of this year’s outbreak.  

Professor Robert Booy, an infectious diseases paediatrician and former head of clinical research at the National Centre for Immunisation Research and Surveillance, told TMR he was more optimistic. 

“I doubt this year’s rise will be as impressive, given the recent community immunity induced by last year’s outbreak,” he said.  

“There’s no surge of people returning from the northern hemisphere either.” 

Influenza and covid continue to be the most prevalent viruses circulating in the Australian population, although flu numbers dropped in the most recently reported fortnight (17-30 April). 

This year there have been more than 32,000 notifications to the National Notifiable Diseases Surveillance System in Australia, more than 6000 of them diagnosed in the fortnight to 30 April.  

There have been 32 influenza-associated deaths this year. 

Children continue to be the worst hit, with notification rates highest in those aged five to nine, followed by those aged four and under and the 10 to 14-year-olds. 

“Since seasonal surveillance commenced in April 2023, there have been 224 sentinel hospital admissions due to confirmed influenza, of which 16 (7%) were admitted directly to ICU,” said the report. 

Influenza A is the dominant strain, accounting for 77% of lab-confirmed cases. 

This year’s vaccine appears to be a good match to circulating strains. Of the 561 samples referred to the WHO collaborating centres this year, “94.8% of influenza A(H1N1) isolates, 76.6% of influenza A(H3N2) isolates, and 99.1% of influenza B/Victoria isolates characterised were antigenically similar to the corresponding vaccine components”. 

In the reported fortnight, GPs were seeing influenza-like illnesses in 2.3 per 1000 patient encounters, a slight increase on the previous fortnight, but down on the three per 1000 reported in week 10. 

So far in 2023, patients presenting to sentinel GPs who were tested for respiratory viruses, 57.7% (120/208) tested positive for a respiratory virus. The most common virus reported was rhinovirus (37.5%). Other viruses detected included influenza (21.7%), SARS-CoV-2 (20.8%), RSV (8.3%), parainfluenza type-2 (3.3%), and adenovirus (2.5%). 

NSW (10,417 notifications) and Queensland (9233) have had the most lab-confirmed notifications this year, while the Northern Territory rate per 100,000 population (457) outstrips the others so far this year. 

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