Australia has begun trapping and vaccinating thousands of wild, apparently healthy little penguins against H5N1 avian flu in what Victorian officials say is the largest wild-bird vaccination program ever undertaken.

Up to 5,000 little penguins at Phillip Island and St Kilda are being targeted for vaccination, and because the vaccine requires two doses, officials will have to catch the flightless birds, vaccinate them, and then catch them again for their boosters.

Buried in the Victorian government's own announcement for the experiment is the state's own admission that “vaccination won’t stop H5 bird flu from circulating.” Instead, officials say the shots may help reduce the virus's impact alongside biosecurity, surveillance and other wildlife measures.

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When the program was announced, Victoria said there had never been a confirmed H5 detection in a little penguin anywhere in Australia. Yet just three days after the vaccination plan was announced, the first little penguin found dead with H5 bird flu was reported on Phillip Island.

The bird tested positive for the virus, though that alone does not establish that it died from it.

The existence of H5N1 in wild birds itself isn't surprising. Wild aquatic birds are natural hosts of influenza A viruses, and H5N1 has circulated extensively through wild-bird populations around the world.

What deserves considerably more attention is the role naturally acquired immunity may already be playing in exposed populations — and whether authorities conducted serological testing to determine that before embarking on mass wildlife vaccination.

Despite increasingly alarming headlines surrounding bird flu, Australia's own Department of Health says the current risk to people in Australia remains low, while the federal agriculture department says avian influenza primarily affects birds and infects humans only on rare occasions.