For most Australians, diphtheria is a ghost of medical history—a name found in old textbooks or mentioned in passing when discussing the triumphs of early 20th-century medicine. Between 1926 and 1935, the disease claimed more than 4,000 lives across the country, acting as one of the leading causes of childhood death globally. It was a terrifying era of “the strangling angel,” where children could succumb to respiratory failure in a matter of days.
The introduction of vaccinations in the 1930s effectively broke the disease’s hold. By the 1950s, diphtheria had become a rarity in Australia, eventually fading into near-obscurity. For decades, the public health victory was so complete that the disease was largely forgotten and with that forgetting came a dangerous decline in vigilance.
Now, that ghost is returning. Recent data reveals a worrying resurgence of diphtheria in Northern Australia, with clusters appearing in the Northern Territory and Western Australia. While many of these cases are less severe skin infections, the return of the respiratory form—the version that historically killed hundreds—serves as a stark reminder that medical progress is not a one-way street. When vaccine coverage slips, the diseases we thought we had defeated simply wait for an opening.
As a physician, I find the current trend particularly concerning not just because of the cases themselves, but because of the fragility of our current defense system. The resurgence is not merely a fluke of geography; it is a symptom of a broader, post-pandemic erosion of routine immunization schedules.
The Two Faces of Diphtheria
Diphtheria is caused by toxins produced by the bacteria Corynebacterium diphtheriae or Corynebacterium ulcerans. Depending on where the bacteria settle, the disease manifests in two distinct ways: respiratory and cutaneous.
Respiratory diphtheria is the most dangerous. It begins with familiar symptoms—fever, sore throat, and a general sense of malaise. However, it quickly progresses to a hallmark clinical sign: the formation of a thick, greyish-white membrane over the tonsils and throat. This membrane is not just a coating; it is a mass of dead cells and bacteria that can physically block the airway, leading to death by asphyxia.
Even if a patient survives the initial respiratory crisis, the toxin can migrate. In the days or weeks following the infection, it can cause myocarditis (inflammation of the heart muscle) or polyneuropathy (nerve paralysis), both of which can be fatal.
Cutaneous diphtheria, by contrast, presents as chronic skin ulcers that refuse to heal. While these sores are generally not fatal, they act as dangerous reservoirs. A person with cutaneous diphtheria can spread the bacteria to un-immunized or partially immunized individuals, who may then develop the lethal respiratory form of the disease.
| Feature | Respiratory Diphtheria | Cutaneous Diphtheria |
|---|---|---|
| Primary Site | Nose, throat, and airway | Skin surfaces |
| Key Symptom | Grey-white throat membrane | Non-healing skin ulcers |
| Severity | High (risk of asphyxia/heart failure) | Lower (primarily a source of spread) |
| Transmission | Respiratory droplets (coughs/sneezes) | Direct contact with sore fluid |
A Fragile Safety Net
The current outbreaks highlight a critical vulnerability in global health: the shortage of diphtheria antitoxin. While antibiotics are used to clear the bacteria and stop transmission, the antitoxin is the only tool capable of neutralizing the circulating toxin in the bloodstream. Once that toxin enters the host’s cells, the damage is irreversible.
Because diphtheria became so rare in the West, global production of the antitoxin plummeted. We now face a scenario where stockpiles are low and manufacturing capacity is minimal. This creates a terrifying clinical reality: even with modern medical intervention, up to one in ten people with respiratory diphtheria may still die.
The catalyst for this resurgence is a measurable drop in vaccine uptake. In 2022, an unvaccinated toddler from the Far North Coast of New South Wales was diagnosed with respiratory diphtheria, requiring intensive care. It was the first such case in Australia since 1992, and it served as a canary in the coal mine.
The numbers reflect a steady decline. By 2025, routine childhood immunization coverage hit its lowest point in five years. Among 12-month-olds, coverage dropped from 94.8% in 2020 to 90.5% in 2025. For two-year-olds, the dip was even more pronounced, falling from 92.1% to 88.4%.
Why the Decline in Coverage?
The drop in vaccination rates is rarely the result of a single factor. Instead, it is a combination of practical barriers and psychological shifts. For many families, the challenge is logistical—difficulty attending appointments due to travel distances or time constraints. In remote areas of the Northern Territory and Western Australia, these barriers are amplified.
However, there is also a growing crisis of trust. Vaccine hesitancy has increased over the last year, often driven by a lack of confidence in health provider information. What we have is exacerbated by a strained primary care system. Parents frequently report that consultations with GPs are too short to address their concerns, and high out-of-pocket costs make these essential conversations inaccessible.
To reverse this, the focus must shift toward investment in primary care. We need funding models that compensate providers for the time required to have empathetic, detailed discussions about vaccines. Medical expertise is only effective if the patient trusts the person delivering it.
Protecting Yourself and Your Family
Diphtheria is entirely preventable. The vaccine is administered as part of the combined DTP (diphtheria, tetanus, and pertussis) shot. In Australia, the schedule is rigorous for a reason: doses at two, four, six, and 18 months, followed by boosters at four years and early adolescence. It is also recommended during each pregnancy and as a booster for adults around age 50.
It is a common misconception that childhood vaccines provide lifelong immunity. By middle age, at least half of the population will have antibody levels too low to protect against the disease. A booster dose is the only way to restore this shield.
If you are unsure of your status, you can check your Australian Immunisation Records via the myGov app or by contacting your health provider. For children and adolescents under 20, catch-up vaccinations are free at community health clinics and Aboriginal medical centres.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
Public health officials continue to monitor the clusters in the Northern Territory and the Kimberley region, where recent months have seen 17 respiratory and 60 cutaneous cases in the NT, and 27 cases in the Kimberley. The next critical checkpoint will be the release of the 2026 national immunization coverage reports, which will determine if the current decline has stabilized or if further targeted vaccination campaigns are required to prevent a wider national outbreak.
Do you have questions about your vaccination schedule or experiences with accessing primary care? Share your thoughts in the comments below.
