Key points
- 221 confirmed diphtheria cases across four Australian states in 2026 (NT, WA, SA, QLD)
- The Northern Territory has the largest share with 133 cases, most in outer regional and remote areas
- Over 94% of cases reported in 2026 are among Aboriginal and/or Torres Strait Islander people
- Australia's immunisation rates are high compared with countries in recent outbreaks - vaccination rates alone don't explain it
- The triple antigen (Adacel, Boostrix) is the key diphtheria-relevant vaccine for travellers to keep current
The forgotten disease, revisited
In February 2024 we wrote about a large outbreak of diphtheria in Africa.
According to the World Health Organisation (WHO), more than 57,000 cases were reported and over 2000 deaths. It was a multi country outbreak with Nigeria, Guinea and Niger the most affected.
We called it the "forgotten disease" and recommended travellers to the region make sure their triple antigen (adacel, boostrix) immunisation was current.
The outbreak received very little attention in Australia. Why would it matter to us? These are low-income countries (gross national income of less than $1085 per capita annually) with vaccination rates for the third triple antigen of less than 60%. Outbreaks might be expected.
On the other hand, Australia is a high-income country with high immunisation rates. Diphtheria outbreaks shouldn't happen.
An outbreak in the Northern Territory
In early April 2026, Healthy Travel reported on an outbreak of diphtheria in the Northern Territory.
Diphtheria is not unusual in the top end but the difference in this outbreak was the nature of the disease. There were four cases of respiratory diphtheria. Cases of cutaneous diphtheria are not unusual but respiratory diphtheria had not been reported for more than 30 years.
The current picture from Australian CDC
According to Australia's newly launched Centre for Disease Control, a total of 221 cases have now been confirmed across 4 state jurisdictions this year (to May 22, 2026) - NT (133), WA (79), SA (6) and QLD (3). Cutaneous cases (67.9%) still outnumber respiratory cases (31.7%) with one undefined. Most cases (96.8%) are classified as residents in outer regional or remote and very remote areas. Over ninety-four percent of the cases reported in 2026 are among Aboriginal and/or Torres Strait Islander people.
Immunisation rates were high when compared with those observed in countries with significant outbreaks of diphtheria in the last 3 years.
What are the likely contributing factors responsible for the current outbreak? Vaccination rates are very important but cannot be viewed in isolation. What about environmental factors and antibiotic resistance? Hopefully these questions will be answered by Australian CDC in coming weeks.
Lessons from the African outbreak
Other factors were considered in the African outbreak 2 years ago:
In February 2024, WHO reported on the diphtheria outbreaks in the African region. The report highlighted the importance of immunization rates but also alluded to other contributing factors including housing and crowding. Can this occur in a high-income country such as Australia?
Read the full WHO report: Diphtheria outbreaks: comprehensive guidance for public health preparedness and response.
What is diphtheria?
Diphtheria is caused by a bacterium, Corynebacterium diphtheriae. The bacteria produce a toxin which can have life threatening effects on the upper airway. It is also responsible for serious systemic effects on the body. These include myocarditis, and kidney damage. Humans are the only reservoir of the disease and transmission can occur through respiratory droplet infection or via direct contact with the skin. It can also be transmitted by raw milk.
Diphtheria was a common cause of death in children prior to the 1950's. It is now very rare. This is largely due to our very successful national immunization program (NIP). Cases of diphtheria are more likely to enter Australia from overseas and this is where secondary prevention is necessary.
Contacts of a case are monitored for illness, and swabs are taken from the upper airway. A vaccine booster is given if they are not up to date. Health Departments have the right to pursue contacts of cases.
Diphtheria is a notifiable disease in Australia.
How is it prevented?
Primary prevention is by vaccination. Diphtheria is a component of the Infanrix hexa, or Vaxelis vaccine. It is given in the first year of life. A child is born with the mother's immunity and this wanes over time. Doses of the vaccine are given at 2, 4 and 6 months with a booster of a diphtheria containing vaccine at 4 years. This provides the child with their own immunity.
It is also a component of the triple antigen (diphtheria/ tetanus/ pertussis). This is often given after an injury (for the tetanus component) or in the 3rd trimester of pregnancy (for the whooping cough component). These "other doses" help to keep the community herd immunity high, locking out potential transmission.
Individuals are often reminded to review their routine immunisations when travelling. A common one is tetanus. It is fortunate that diphtheria, tetanus and whooping cough can all be updated in one vaccine (Adacel, Boostrix).
Travelling overseas and not sure if your triple antigen is current? Book a telehealth consultation with one of our Australian travel doctors.
Diphtheria is also available in combination with tetanus, whooping cough and polio (Adacel polio, Boostrix IPV) and might be considered for travellers to regions where vaccine associated polio is being reported (as of 30 March 2026).
See the current tracker: circulating vaccine-derived poliovirus count.
Wild polio is only being reported in Pakistan and Afghanistan.
