Bird flu threat ‘very low’ for humans: CSIRO

Experts from the CSIRO’s Australian Centre for Disease Preparedness (ACDP) say the threat of the H5N1 bird flu spreading to humans remains ‘very low’, following Australia’s first recorded mass bird mortality event last week.
 
It comes as the Federal Government moves to vaccinate all native birds in captivity and Victorian authorities prepare to vaccinate around 5000 little penguins at Phillip Island and St Kilda, in an effort to stem the predicted mass mortalities.
 
H5N1 had been detected in every continent except Australia and greater Oceania until June, when the first Australian case was confirmed in a brown skua seabird in Western Australia.
 
ACDP Director Dr Debbie Eagles said for GPs, most guidance would come from epidemiological information.
 
‘That might be that people present with flu-like symptoms and report exposure to wild birds that have been sick, potentially ones that have tested positive,’ she said.
 
‘So, people who have been involved in what might be considered high-risk activities, such as direct contact with sick or wild birds.’
 
She said the whole genome sequence testing the ACDP conducts ‘can help identify the source of the virus, identify changes as we get more detections, can help characterise local transmission events and look for reassortment with influenza viruses that are already circulating in Australian birds.’
 
ACDP Senior Research Scientist Dr Frank Wong confirmed there has not been any recorded human cases of the disease in Australia related to this outbreak.
 
He said an ‘ecological perfect storm’ would be required for the virus to spill over, but that did not mitigate the need to stay on high alert.
 
Dr Wong added that most recorded cases in humans have presented as mild respiratory infections and/or conjunctivitis, with just two being more severe illness ‘and they were linked to people who were either elderly or had predisposing conditions’.
 
‘The risk is very low and remains very low for transmission between birds and people. And that’s what we’ve seen internationally over the last few years with this strain,’ he said.
 
He said since 2024–25, there was a spike in human infections in the United States, the majority linked to infected dairy farms, and two outbreaks in poultry farms.
 
‘Exposure is with people in professions that expose themselves to outbreak environments,’ Dr Wong said. 
 
However, he stressed that they were from a different genotype to the H5N1 virus that is seen in Australia.
 
‘To date, there’s no clear predictor for the ability of these viruses to jump from birds to mammals, and from birds and mammals to humans,’ Dr Wong said.
 
‘Even in cases where we’ve found the virus in either mammals or humans, the majority of the viruses that are isolated from these cases, it’s still very much an avian-adapted virus, with the majority avian genetic signatures.’
 
He said people in high-risk occupations ‘should get vaccinated with the standard flu vaccine’
 
A recent British study of 428 people working with, or exposed to, birds infected with influenza A (H5N1) clade 2.3.4.4b viruses (primarily poultry sites), found low rates of human infection among participants.
 
Beginning in 2023, the original study cohort included only asymptomatic people exposed to infected birds, while those with respiratory symptoms were recruited from January 2024 onwards. 
 
Less than 1% of participants met the study’s criteria for infection, resulting in two confirmed cases and one unclear case. No severe illness was reported; two of the six PCR-positive participants had mild symptoms.
 
Full personal protective equipment was worn by 85% of participants, who self-reported consistent use, with no breaches, while within the biosecurity area.
 
Only 19% reported having received an influenza vaccination.
 
The researchers noted that although seasonal influenza vaccines do not offer protection to humans against zoonotic influenza, ‘they should be considered for those occupationally exposed to zoonotic influenza to reduce the risk of co-infection and thus reassortment events’.
 
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