Urgent vaccine warning after NT's diphtheria outbreak crosses three state borders

The nation's top medical body is urging all Australians to ensure they are fully vaccinated and boosted against diphtheria amid the country's "biggest outbreak in decades".

A resurgence of the almost-eradicated, highly contagious disease in the Northern Territory has now spread across three state borders, with a total of 223 confirmed cases to date.

One person in the Territory has died, although the exact cause of death remains under investigation.

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The Australian Medical Association has today issued a statement calling on everyone to check that they and their families are up-to-date with their diphtheria vaccinations.

Children are typically immunised against the potentially-deadly disease as part of the National Childhood Immunisation Program at two, four and six months.

Routine boosters are also recommended for adolescents and adults in certain circumstances.

"Immunisation is one of the greatest achievements in modern medicine, but when vaccination rates fall, serious diseases, which we had largely eliminated, can make a come back," Australian Medical Association President Dr Danielle McMullen said.

"We are seeing that risk play out with diphtheria."

It's believed a drop in childhood vaccination rates globally following the COVID-19 pandemic may be contributing to the current resurgence.

The number of fully vaccinated children in Australia has been creeping downwards since reaching record highs in early 2020, with the number of two-year-olds who are fully vaccinated dropping below the crucial threshold of 90 per cent in 2024.

By the end of last year, the number of babies who were receiving the triple vaccine that protects against diphtheria on time had fallen to 79.7 per cent.

This means the number of babies who were left unvaccinated or were vaccinated late had almost doubled since the start of 2020.

Where is the current outbreak?

The current diphtheria outbreak began in remote Aboriginal communities in the Northern Territory, but has now spread across all five regions of the NT.

Genomic sequencing of the current strain has been linked to smaller pockets of outbreaks in WA's Kimberley region and North Queensland in 2024 and 2025.

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As of yesterday, the Territory had recorded 133 cases of diphtheria, prompting a major push to increase vaccination rates amongst those in the hardest-hit Indigenous communities.

Western Australia is also facing a growing outbreak in the Kimberley, with 79 people confirmed to have the illness.

Now, it's been confirmed that diphtheria has also spread across the South Australian and Queensland borders, with six and five cases recorded in those states respectively.

"This is probably the biggest diphtheria outbreak we've seen - certainly for decades," Health Minister Mark Butler said yesterday.

"There's no question this is serious."

Butler said "almost all" of the current cases in the NT were Indigenous Australians and the government was working with the Aboriginal-controlled sector to increase vaccination rates in those communities.

Head of Immunisation and Health Systems Strengthening at Burnet Institute, Dr Milena Dalton, said the scale of the current outbreak was "deeply concerning".

"This is no longer an isolated outbreak, and it highlights how quickly vaccine-preventable diseases can re-emerge when there are immunity gaps," she said.

So what exactly is diphtheria?

For decades, diphtheria was among the leading causes of death in Australian children, killing more than 4000 Australians between 1926 and 1935 alone.

However, a vaccination drive starting in the 1930s brought it close to eradication by the 1950s.

Diphtheria is caused by toxins produced by certain strains of Corynebacterium bacteria.

Early symptoms are similar to that of a cold or flu, including a fever and sore throat, but over a few days, respiratory diphtheria will progress and a greyish-white membrane may form over the throat and tonsils, making it difficult to swallow or breath.

Severe cases of respiratory diphtheria can cause the throat and neck to swell which blocks the airways and impacts breathing, potentially resulting in death from asphyxia.

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The bacterial toxin can also damage the heart, kidneys, brain and nerves.

The less severe form of diphtheria, cutaneous diphtheria, causes skin ulcers that won't heal.

This form of diphtheria generally isn't life-threatening but these sores are a source of bacteria that spread the disease, causing vulnerable or unvaccinated people to develop the respiratory disease.

The bacterial toxin can also damage the heart, kidneys, brain and nerves.

Spread through respiratory droplets from coughing and sneezing as well as the skin sores, diphtheria is highly infectious.

How is it treated?

Diphtheria is preventable with vaccination, which stimulates the body to produce antitoxins that protect against diphtheria toxin.

However, once someone has been infected, vaccination will not protect them.

Prompt treatment with antibiotics can help clear the organism and a diphtheria antitoxin is also used to treat respiratory diphtheria.

However, once the toxin has entered host cells, its effects are no longer reversible.

Even with treatment, up to one in ten people with respiratory diphtheria will die.

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