By the National Reporting Team's Suzanne Dredge and Philippa McDonald
Updated Sun at 7:47pm
Sun 23 Aug 2015, 7:47pm
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The CSIRO scientist who developed the Hendra virus vaccine is recommending fewer injections be given to horses to protect against the deadly illness.
Currently boosters have to be given every six months and horse owners have told the ABC they fear their horses are becoming ill and in several cases dying as result of "over-vaccination".
"At the moment the evidence we have is that after the six-month booster you can maintain levels of protection in horses for at least a further 12 months, possibly even longer," CSIRO's Deborah Middleton said.
"I certainly have sympathy for owners who feel their horses are being over-medicated because I think any vaccination carries the risk of a vaccine reaction and all the more reason to be very certain that we're only giving horses the minimum number of vaccines we need to give them protection against Hendra virus."
Vaccine manufacturer Zoetis' veterinary operations manager, Richard L'Estrange, said the industry would support changing the interval between vaccinations from six months to 12.
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"I think everyone would like to see that change made and everyone would like to see that change made as soon as possible, but we need to allow the regulator to make their assessment and they will give us their answer in due course," Mr L'Estrange said.
Sadly for us it hasn't been an easy road ... I think at last count it was about 60 odd horses vaccinated here, sadly two are dead.
Natalie Roach
In a statement to the ABC, the Australian Pesticides and Veterinary Medicines Authority (APVMA) said it would require solid evidence to consider making any change.
"To support an application for a 12-month vaccination interval, Zoetis would need to make an application to the APVMA with evidence that horses retain sufficient immunity 12 months after vaccination," the statement said.
Queensland is a known Hendra zone, as are areas of northern New South Wales.
There have been two recent outbreaks of the Hendra virus in Queensland and a total of 50 outbreaks in the past 20 years in both states.
Four people have died along with 90 horses.
Seven horse owners had to be treated for potential exposure to the bat-borne virus last year.
While the virus was identified in 1994, a vaccine was not available until November 2012.
Since it was registered earlier this month, 380,000 doses have been given to 110,000 horses.
Brisbane vet Nathan Anthony has vaccinated 5,000 horses at his practice.
"We have only seen minor reactions at the injection site so this is some swelling and some sort of pain," Dr Anthony said.
"The odd horse can develop a fever for a couple of days but it's not occurring very commonly and it is similar to that we experience when we have a tetanus injection or [when] we vaccinate our kids."
But on the mid-north coast of New South Wales, which is just south of a known Hendra zone, several local horse owners are reporting a cluster of horse deaths and debilitating illnesses which they fear are from multiple doses of the Hendra virus vaccine.
Horse owners say Hendra vaccine killed healthy horses
Natalie Roach, who runs an equestrian centre near Wauchope, has had horses who had been vaccinated die.
"Sadly for us it hasn't been an easy road ... I think at last count it was about 60 odd horses vaccinated here, sadly two are dead," Ms Roach said.
"My son's little pony has had three bouts of extreme laminitis [inflammation in the hoof] and now he's useless to us."
Ms Roach said she believed the vaccination was to blame, but Zoetis conducted tests at the property and denied the vaccine was the cause of death.
"Everything they tested for was coming back negative," she said.
"They walked the paddocks checking for weeds that could be toxic to the horse, they looked at the feeds and basically came back to us saying 'there's no toxic plants, there's nothing there'."
Closer to Port Macquarie, Sue Vickery said her horse Bart was no longer able to be ridden and almost died after a sixth dose of the Hendra virus vaccine.
"His mother was Empire Rose, who won the Melbourne Cup. He was a very imposing horse because he was so big and he was very talented," Ms Vickery said.
The stallion became ill the day after a fifth dose of the vaccine.
"His temperature was nearly 40 degrees [Celsius], which is incredibly high for a horse, and that lasted four days," Ms Vickery said.
"He didn't eat anything, he could hardly walk, he was so sick and I thought 'I don't know if this horse is going to make it' and he got over it.
"I didn't realise at the time that his autoimmune system was already partially compromised and by hitting him with the sixth needle [it] made his immune system go completely — [that] is how the vet explained it to me."
Amanda Mulligan's horse, Maestro, was euthanased five weeks after it received a fifth vaccine injection.
"He was standing in a lather of sweat and he had lost everything — there was no weight left on him," Ms Mulligan said.
"We called the vet and he was put on IV with a temperature of 41C. We then noticed he was getting nose bleeds and basically his whole system was shutting down so [we] decided to stop the pain.
"I do believe it was the vaccine. I don't know whether it was the amount that he [had], because he was fine on the first four [or] five."
Regulator confirms link between Hendra vaccine, horse's illness
The APVMA has written to Ms Mulligan acknowledging her horse had a reaction to the vaccine.
The letter said there was a probable link between the vaccine and Maestro's lethargy and malaise.
Matthew Walker, a vet in the southern highlands, said he had received a flood of inquiries from concerned horse owners who wanted their cases reviewed independently.
Mr Walker is currently examining more than 40 cases connected to Hendra vaccinations.
"I think there should be a more in-depth investigation of deaths or serious diseases," he said.
"If your treatment is potentially more deadly than the disease, this is the balance you've got to strike."
Mr L'Estrange said the vaccine was highly safe and effective.
"Fortunately with this particular vaccine, the adverse event rate has been very low, we see adverse events reported for about 1 in every 350 doses of vaccine administered," he said.
"In terms of doses administered to horses prior to registration, no, this would be the most scrutinised product in veterinary history in this country and it's been given the tick of approval by the regulator."
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