Australia’s largest diphtheria outbreak in decades: Why vaccination still matters

Australia is currently experiencing its largest diphtheria outbreak in decades, with more than 230 confirmed cases reported across the Northern Territory, Western Australia, South Australia, and Queensland (Australian Centre for Disease Control, 2026). Health authorities have warned that numbers may continue to rise, with the outbreak now considered the largest recorded since national records began in 1991 (Australian Broadcasting Corporation, 2026).

For many Australians, diphtheria may seem like a disease of the past, something rarely seen thanks to successful vaccination programs like the National Immunisation Program (Australian Government Department of Health and Aged Care, 2026). However, this outbreak is a reminder that vaccine-preventable diseases can quickly re-emerge when immunity levels within communities decline.

What is diphtheria?

Diphtheria is a highly contagious bacterial infection caused by Corynebacterium diphtheriae (Department of Health, Disability and Ageing, 2025). It can affect both the respiratory tract and the skin.

Respiratory diphtheria can present with:

• sore throat
• fever
• difficulty swallowing
• swollen neck glands
• a thick grey or white membrane in the throat.

In severe cases, the toxin produced by the bacteria can lead to airway obstruction, heart complications, neurological damage, paralysis, and even death. Cutaneous diphtheria affects the skin and may appear as chronic infected sores or ulcers (NSW Health, 2026). While often less severe, it can still contribute to transmission within communities (World Health Organization, 2023).

Even with treatment, approximately 1 in 10 people with respiratory diphtheria may die from the disease (Australian Centre for Disease Control, 2025).

The statistics behind the outbreak

The current outbreak has increased rapidly since late 2025, with notifications now almost 30 times higher than the average seen between 2022–2025.

Current Australian data (Australian Centre for Disease Control, 2026) shows:

• Over 230 cases reported nationally in 2026.
• 155 confirmed cases in the Northern Territory alone.
• Around 25–28% of patients have required hospitalisation.
• One suspected diphtheria-related death has been reported in the NT, the first possible fatality in almost a decade.
• Approximately 93–94% of cases in 2026 have occurred among Aboriginal and Torres Strait Islander peoples.

The Australian Centre for Disease Control (2026) has also reported an increase in respiratory diphtheria cases, which are generally more severe than cutaneous infections.

Why are cases increasing?

Health experts have identified several contributing factors behind the outbreak, including:

• Reduced vaccination coverage in some areas.
• Delayed childhood vaccinations.
• Waning immunity in adults overdue for boosters.
• Increased travel and movement between regions.
• Healthcare workforce shortages in remote communities.
• Overcrowded housing and reduced access to healthcare services.

Routine childhood immunisation coverage in Australia fell to its lowest level in five years during 2025 (National Centre for Immunisation Research and Surveillance [NCIRS], 2026a). In the Northern Territory, only 91.9% of five-year-olds were fully vaccinated against diphtheria, below the 95% target generally considered necessary for strong community protection (NCIRS, 2026b; AIHW, 2024).

Among adolescents, coverage has also declined:

• Only 82.6 per cent of First Nations adolescents had received their adolescent diphtheria-tetanus-pertussis (dTpa) vaccine dose in 2022.
• NCIRS (2026a) data also found that 1 in 4 Aboriginal and Torres Strait Islander children received their second diphtheria-containing vaccine dose late in 2024.

Vaccination remains our strongest protection

The good news is that diphtheria is largely preventable through vaccination.

The diphtheria vaccine is included in Australia’s National Immunisation Program and has been highly effective in preventing severe disease for decades (Australian Government Department of Health and Aged Care, 2026). However, immunity can decrease over time, which is why booster vaccinations remain important throughout adulthood (Australian Institute of Health and Welfare [AIHW], 2024).

Healthcare workers, parents, carers, and adults who are unsure of their vaccination status are strongly encouraged to speak with their healthcare provider to determine whether they are due for a booster (NSW Health, 2026).

Vaccination not only protects individuals, it also helps protect vulnerable members of the community, including infants, older adults, immunocompromised people, and those unable to receive certain vaccines.

The role of nurses during outbreaks

Nurses are often at the frontline of public health responses and are uniquely positioned to support communities during outbreaks.

This includes recognising and escalating suspected cases promptly, supporting infection prevention measures and promoting vaccination uptake.

One of the greatest challenges during outbreaks is the rapid spread of misinformation online. Social media platforms can expose people to conflicting messages about vaccine safety, effectiveness, and necessity. This can understandably create fear, confusion, and mistrust.

As healthcare professionals, nurses play an important role in helping patients navigate this information in a respectful, non-judgemental, and evidence-based way. Compassionate education and therapeutic communication remain essential nursing skills.

The current outbreak is a reminder that public health is everyone’s responsibility. Maintaining vaccination coverage and supporting community education are key steps in preventing further spread.

References

Australian Broadcasting Corporation. (2026, May 20). Health officials warn cases of diphtheria could rise. Abc.net.au. https://www.abc.net.au/news/2026-05-20/health-officials-warn-diphtheria-could-increase-in-outbreak/106700432

Australian Centre for Disease Control. (2025, December 18). Diphtheria. Australian Centre for Disease Control. https://www.cdc.gov.au/diseases/diphtheria

Australian Centre for Disease Control. (2026, May 21). Diphtheria outbreak update. Australian Centre for Disease Control. https://www.cdc.gov.au/newsroom/news-and-articles/diphtheria-outbreak-update

Australian Government Department of Health and Aged Care. (2026). National Immunisation Program schedule. Australian Government Department of Health and Aged Care. https://www.health.gov.au/resources/publications/national-immunisation-program-schedule?language=en

Australian Institute of Health and Welfare. (2024, July 2). Immunisation and vaccination. Australian Institute of Health and Welfare. https://www.aihw.gov.au/reports/australias-health/immunisation-and-vaccination

Department of Health, Disability and Ageing. (2025). Diphtheria. The Australian Immunisation Handbook. https://immunisationhandbook.health.gov.au/contents/vaccine-preventable-diseases/diphtheria

National Centre for Immunisation Research and Surveillance. (2026a, April 19). “Tens of thousands of young children unprotected” as immunisation coverage hits five-year low in Australia. NCIRS. https://ncirs.org.au/tens-thousands-young-children-unprotected-immunisation-coverage-hits-five-year-low-australia

National Centre for Immunisation Research and Surveillance. (2026b, April 30). Before vaccines, diphtheria used to kill hundreds each year. Now it’s back in Australia. NCIRS. https://ncirs.org.au/vaccines-diphtheria-used-kill-hundreds-each-year-now-its-back-australia

NSW Health. (2026). Diphtheria. Nsw.gov.au. https://www.health.nsw.gov.au/Infectious/diphtheria/Pages/default.aspx

World Health Organization. (2023, November 20). Diphtheria. Www.who.int. https://www.who.int/news-room/fact-sheets/detail/diphtheria