The NSW government has identified little penguins and critically endangered regent honeyeaters as priority species for bird flu vaccination, after the state’s fifth case of the deadly virus was confirmed on Saturday in a greater crested tern found dead near Eden on the South Coast.

At least 50 birds of the same species died in a mass mortality event in South Australia earlier this month.

With increasing deaths and the detection of the virus in a “Typhoid Mary” superspreader species, attention is starting to shift from individual sick or dead birds to monitoring for mass die-offs and detecting shifts in the virus’s genetics.

A Victorian plan to vaccinate 5000 little penguins on Phillip Island did not move fast enough, with news of a penguin dying from the disease breaking on Saturday.

The NSW government said plans to inoculate captive little penguins and regent honeyeaters in the state were on track but awaiting approval from the national Animal Health Committee.

The government is working with organisations including Taronga Zoo, which breeds regent honeyeaters for wild release. Fewer than 400 exist in the wild.

While the vaccine can reduce mortality, it’s not known exactly how well it protects native birds, and experts warn vaccines alone can’t stop ecological catastrophe. The government has acknowledged there is little data about the vaccine’s effectiveness outside of poultry.

“It is not a silver bullet. The vaccine cannot be the only weapon to control the virus and containment of outbreaks. It’s a supplementary tool,” bird flu expert Dr Ariful Islam from Charles Sturt University said.

Last year, the government commissioned trials at CSIRO’s Australian Centre for Disease Preparedness to establish dose rates for small native bird species.

Further pilot studies tested the safety of the vaccine – which was developed for poultry – in other captive natives including penguins, ratites (emus and cassowaries), raptors, owls, shorebirds, ducks, cockatoos and other parrots.

When asked for efficacy data, a spokesperson from the Department of Agriculture, Fisheries and Forestry said “results to date have been encouraging and have informed regulatory assessments and emergency use arrangements for the vaccine”.

The spread of the virus into silver gulls in South Australia has sparked fears of widespread infection among native birds.

Bird ecologist Professor Anne Peters, from Monash University, dubbed the notorious fish-and-chip thieves the “Typhoid Mary” superspreaders of bird flu because they range widely between cities, the coast and inland areas.

Infected ducks, meanwhile, can carry the virus far without falling ill. “Finding active viruses in birds that aren’t sick at all would also be extremely worrying,” Peters said.

“Unfortunately, very many of our birds but also mammals, for example seals and sea lions, but also dolphins, are known to be at great risk of mass mortalities.”

Experts have called for greater action to protect marine mammals, including the endangered Australian sea lion.

A trial in the US showed a vaccine developed for cows safely generated antibodies in elephant seals, suggesting existing vaccines might be adapted to protect pinnipeds. Australian authorities are monitoring those trials.

Professor Euan Ritchie, an ecologist at Deakin University, questioned why the government hadn’t capitalised on the five-year head start Australia had before the virus arrived to invest in developing our own vaccine to protect the nation’s globally unique mammals.

“If [a mammal vaccination] is possible, and it’s only been limited by investment, then the government would need to answer to Australians why that hasn’t been a priority,” he said.

Delivering the two required vaccine doses to many wild species is not feasible, but it’s theoretically possible to target some threatened animal populations such as sea lions, Ritchie said.

“In some cases, like the Tasmanian devil, they have small populations and they’re range-restricted, so it’s not outside the realm of possibility to entertain a vaccination program.”

The genotype of H5 bird flu hitting Australia, called B3.2, ripped down the entire west coast of South America in just six months before jumping into the sub-Antarctic, according to CSIRO.

“[It caused] great impact to South American poultry industries as well as to wild bird life and to marine mammals, so that’s why we’re concerned about the introduction of this virus to Australia,” Dr Frank Wong from the agency’s Australian Animal Health Laboratory said.

The genotype is different to the strain of the virus that has circulated in dairy cows and sickened humans in the US.

CSIRO released a pre-print paper last week using genomic data to track how the virus spread from South America across the sub-Antarctic to Australia.

The agency is now monitoring the virus for changes, including re-assortment with local low-pathogenic bird flu, which could increase infectiousness, and mutations in a gene called PB2.

“In other parts of the world, when this virus has got into mammals, there’s certain particular nucleotides in the gene which change and allow that virus to infect mammals more readily,” Dr Matthew Neave from CSIRO said.

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