Diphtheria was once one of Australia’s most feared childhood infections, killing thousands of children before vaccines were available. Then for decades, it became so rare most doctors never saw a case.

That has changed. Diphtheria has reappeared in parts of Australia, with cases reported in the Northern Territory, Western Australia, South Australia and Queensland.

In 2026, there have been just over 230 cases, largely in the Northern Territory, which makes this Australia’s biggest outbreak since national records began.

On Thursday, the federal government announced a $7.2 million package to respond to the outbreak.

But diphtheria is just the latest infectious disease to make a comeback in Australia.

Once, diphtheria, measles, scarlet fever and whooping cough were feared diseases. But in two generations, improved living conditions, better sanitation and vaccination means these and other infectious diseases are no longer part of everyday life for most Australians.

But as we’re seeing, those gains can be fragile.

Public health experts use three different terms for reducing levels of disease. Control means bringing cases down to a low level through ongoing measures; elimination means stopping ongoing local transmission in a defined geographic area, such as a country or region; and eradication means removing a disease from the planet entirely.

As an example of elimination, the World Health Organisation declared Australia measles-free in 2014. Eradication of a disease is much harder, and has been achieved for human disease only once – with smallpox in 1980.

But these achievements are not permanent. Infectious diseases can re-emerge when vaccination........

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