A large diphtheria outbreak is currently affecting the Northern Territory, Western Australia, Queensland and South Australia.
Between 1 January and 26 May 2026, at least 248 cases were notified nationally, making this one of the largest outbreaks in decades. Importantly, more than 94% of cases have occurred among Aboriginal and Torres Strait Islander people. No cases have been reported in NSW so far in 2026. Australia’s Chief Medical Officer declared the outbreak a communicable disease incident of national significance (CDINS) on 22 May 2026, to improve the outbreak response coordination between the federal and state and territory governments.
Diphtheria is caused by the bacteria Corynebacterium diphtheriae or Corynebacterium ulcerans. It commonly affects the upper respiratory tract, presenting with sore throat, low-grade fever and enlarged lymph nodes in the neck. Within 2–3 days, an adherent grey membrane may form over the throat, leading to difficulty swallowing and breathing. Severe complications can include paralysis and pneumonia, and the disease can be fatal.
Cutaneous form of diphtheria, more common in tropical regions, presents as shallow skin ulcers covered by a greyish membrane which are often slow to heal. In the current outbreak, over two-thirds of cases have been cutaneous infections, while around one-third have been respiratory. Approximately one quarter of all cases have required hospitalisation.
Diphtheria spreads through respiratory droplets (e.g. coughing and sneezing) and close contact with infected individuals, including those without symptoms. Transmission can also occur via contact with contaminated surfaces, skin lesions, or items such as tissues or clothing. Good hygiene practices are therefore essential to reduce spread.
Treatment involves antibiotics and, in more severe cases, administration of diphtheria antitoxin. Vaccination with diphtheria-toxoid vaccine remains the key preventive measure. While vaccination is highly effective at preventing severe, toxin-mediated disease, it does not reliably prevent infection or transmission.
Under the National Immunisation Program (NIP), children are recommended to receive five doses of diphtheria-containing vaccine at 2, 4, 6 and 18 months, and at 4 years of age, with a booster at 11–13 years. Pregnant women are also eligible for a funded dose between 20–32 weeks in every pregnancy.
In response to the current outbreak, NSW Health has implemented a targeted vaccination program, funding Boostrix vaccine for Aboriginal and Torres Strait Islander people who are not eligible under the NIP.
Key actions for ACCHO clinics
Check vaccination status for all patients
Healthcare providers are strongly encouraged to provide opportunistic review of their patients’ vaccination status and ensure vaccinations are up to date.
As part of the outbreak response, NSW Health will:
- Fund additional doses of diphtheria-containing vaccine for Aboriginal and Torres Strait Islander people aged over 20 years who have not received three doses, to complete the primary course (3 doses);
- Fund a booster dose for Aboriginal and Torres Strait Islander people aged over 20 years who have previously received at least three doses, where the most recent dose was more than 10 years ago;
- Fund a booster dose for Aboriginal and Torres Strait Islander people aged 17 years and over who have previously received at least three doses, where the most recent dose was more than 5 years ago AND they are travelling or moving to areas considered at higher risk for diphtheria.
ACCHOs can order Boostrix via the NSW Vaccine Centre using the routine vaccine order form. Please note the funded booster doses are currently only available through Aboriginal Medical Services or General Practices, not through vaccinating pharmacies.
Remain alert for diphtheria
Clinicians should maintain a high index of suspicion, particularly in patients with recent travel to affected regions. For suspected cases:
- Take a throat swab for respiratory presentations;
- Take both ulcer and throat swabs for suspected cutaneous disease.
Aboriginal and Torres Strait Islander patients presenting with sore throat should also receive empiric antibiotic treatment for Group A Streptococcus, in line with current guidelines. Notify your local Public Health Unit of any suspected diphtheria cases on 1300 066 055.
You can find updates on NSW Health response to the outbreak here. You can also download diphtheria immunisation resources at the NACCHO website.
Diphtheria is vaccine-preventable but is re-emerging. Checking and updating vaccination at every opportunity, together with maintaining strong hygiene practices, remains the most important way to protect individuals, families and communities.
