NZ has spent years preparing for H5N1 bird flu. For some species, it may not be enough

The kakī, or black stilt, a native wading bird only found in New Zealand, is considered highly vulnerable to H5N1 avian flu.

Liz Brown , CC BY-NC-ND The arrival of the highly pathogenic H5N1 strain of bird flu in Aotearoa New Zealand last month triggered a national response years in the making .

By then, surveillance systems, species protection plans and even vaccines for some birds were already in place as part of a coordinated approach led by the Ministry for Primary Industries.

Yet even these preparations may not be enough to save some of the country’s rarest birds.

Many survive in tiny, isolated populations with limited genetic diversity .

For these highly vulnerable species, the outcome may depend not only on conservation efforts, but also on chance.

Genetic diversity acts as nature’s insurance policy against disease.

In large populations, some individuals are more likely to survive an outbreak and help the population recover.

But in small, isolated populations with little genetic diversity, those odds are much lower, leaving species far more vulnerable to extinction.

Why vaccines can only do so much H5N1 has caused mass mortality events in wild birds around the world since emerging in 2020, making it one of the most significant disease threats many species have faced in decades.

Vaccines offer one important layer of protection, but they are no silver bullet.

A Department of Conservation-led vaccine trial involving five intensively managed threatened species found that effective protection requires at least two doses administered a few weeks apart.

In kakī – the critically endangered black stilt and one of the world’s rarest wading birds – immunity declined after three months, meaning a third dose will be needed.

With the trial now complete and H5N1 in New Zealand, vaccinations are underway, beginning with 300 individuals from the five species involved in the study.