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Health authorities are urging people to get vaccinated, as a potentially deadly infection spreads across four Australian states.

Diphtheria is a serious infection caused by the toxin-producing bacteria, Corynebacterium diphtheriae. It spreads through contact with an infected person’s bodily fluids – such as droplets produced from coughing or sneezing – or skin sores.

Since January, Australia has recorded more than 220 diphtheria cases, in the worst outbreak the country’s seen in decades. As of Thursday, there were 139 cases in the Northern Territory, 82 in Western Australia, seven in South Australia and three in Queensland.

The federal government has announced a A$7.2 million emergency support package, which aims to boost vaccination rates and strengthen the health workforce in states affected by the current diphtheria outbreak.

So is it still spreading? And should you be concerned?

Remind me, what is diphtheria?

There are two main types of this rare but serious bacterial infection.

Respiratory diphtheria affects the throat and airways, and can be life-threatening if the toxin produced by the bacteria damages the airways, nerves or heart. Even with treatment, up to 10% of people with respiratory diphtheria die.

Cutaneous diphtheria affects the skin, mainly causing skin ulcers on the legs or arms. This form of diphtheria is usually less severe, but contact with wounds is still a common way the infection spreads between people.

It is possible to contract respiratory diphtheria by being exposed to someone with cutaneous diphtheria, and vice versa. For instance, bacteria in one person’s skin sore may cause respiratory diphtheria in another person, if transferred through close contact.

Who’s affected by this latest outbreak?

According to the Australian Centre for Disease Control’s latest report, roughly 94% of cases identified since January 2026 have been Aboriginal and/or Torrest Strait Islander people.

The majority have been cases of cutaneous diphtheria, but around 30% have been cases of respiratory diphtheria.

Authorities are still investigating what factors may be contributing to this outbreak. However, this likely includes waning immunity, lower routine immunisation rates and a higher prevalence of skin infections in affected communities. Other factors such as overcrowding and limited access to health care may also play a role.

The need for vaccines

Vaccination is the best way to prevent severe diphtheria infections, and the further spread of the disease.

Before vaccines were widely introduced in the 1950s, about one in ten people with respiratory diphtheria died from their symptoms. And the risk was higher among young children and the elderly.

In the decades since, very few Australians have died from diphtheria, with authorities recording four diphtheria-related deaths between 1999 and 2025.

That’s largely thanks to the diphtheria, tetanus, pertussis (whooping cough) vaccine, also known as DTP. This combined vaccine protects against the diphtheria toxin.

In Australia, children routinely receive this vaccine at two months, four months, six months and 18 months of age. They also get it when they are four years old, and again in early adolescence.

But it’s also vital adults receive boosters of the DTP vaccine. This is because immunity declines over time even though the vaccine itself is very effective.

Research suggests more than 99% of babies who get the relevant vaccinations develop enough antibodies to fight against the diphtheria toxin. But by middle age, only half of adults maintain these antibody levels if they don’t have a booster dose of DTP.

However, national immunisation data shows vaccine rates have significantly declined, particularly since the COVID pandemic. And just last year, Australia’s childhood immunisation rate dropped to a five-year low.

How often you need a vaccination depends on your age and occupation. But the current health advice is adults should get a DTP booster every ten years, from your early 20s. If you’re unsure when you received your last dose, speak to your GP, community health clinic or Aboriginal Medical Service.

Who needs a vaccine? And how about boosters?

During a diphtheria outbreak, it’s crucial to ensure all children, adolescents and adults aged 50 and above are up to date with routine immunisations.

Importantly, the new advice for Aboriginal and Torres Strait Islander people, and health-care workers in affected communities, is to get a booster vaccine every five years.

Pregnant women should also receive a booster dose 20 to 32 weeks into their pregnancy. This is mainly to reduce their infant’s risk of having whooping cough, but will also protect against diphtheria until they receive their first vaccination.

And additional doses are available to people who have a mild case of diphtheria or are in close contact – living in the same household, for example – with people who already have the infection.

In the current outbreak, an estimated 90% of cases have occurred in people that have already been vaccinated. The vaccine has ensured most of these people only develop mild forms of diphtheria.

But tragically, one person with the disease has since died.

So, should I be worried?

Local, state and territory public health departments are working hard to curb this historic outbreak. This week, both NT Health and WA Health released an outbreak immunisation schedule for people living and working in affected communities.

But if you are in an outbreak area and have a sore throat or any skin sores, visit your local clinic. This will help authorities detect any potential diphtheria cases early. And if you have other symptoms such as fever, breathing or swallowing difficulties or a greyish membrane in your throat, visit an emergency department immediately.

Archana Koirala is chair of the Vaccination Special Interest Group of the Australasian Society for Infectious Diseases.

Bianca Middleton is a member of the Vaccination Special Interest Group of the Australasian Society for Infectious Diseases.