Two diphtheria cases have been linked to West Kimberley Regional Prison in Derby over the past two months, as health authorities grapple with an outbreak affecting parts of regional Western Australia.

Diphtheria, a contagious bacterial infection, can strike the throat and skin. For those unvaccinated or under-vaccinated, the consequences can be fatal.

The Department of Justice confirmed the cases emerged at separate times, each managed by the local public health unit.

West Kimberley Regional Prison sits on the outskirts of Derby, some 220 kilometres north-east of Broome, drawing in male and female prisoners from communities scattered across the Kimberley.

A Department of Justice spokesperson said neither person contracted the infection while inside the prison.

"Neither case acquired their infection while at the prison, and both cases were isolated from others until they returned negative test results," the spokesperson said.

The department's Communicable Disease team has been moving through affected regions, delivering vaccinations to eligible prisoners to contain the spread.

Corrective Services staff have access to state-funded diphtheria vaccines, available through immunisation providers across the Kimberley, Pilbara and Goldfields.

"Staff remain alert to potential diphtheria symptoms among prisoners, with protocols in place to isolate and test any suspected cases," the spokesperson said.

The confirmation arrives as health authorities in Western Australia work to contain a regional diphtheria outbreak, with cases touching communities across the Kimberley and the broader north.

There have been 85 confirmed cases of diphtheria in regional WA since the outbreak began in December 2025.

Health authorities are urging residents in affected regions to check their vaccinations, as public health teams press on with contact tracing, testing and immunisation efforts.

The Department of Justice says its response inside prisons is guided by public health advice.

The cases connected to West Kimberley Regional Prison form part of the wider regional response, though the department maintains there is no evidence either infection was contracted within the facility.