Stochastic models indicate rapid smallpox spread and mass mortality of Indigenous Australians after colonial exposure.

The impact of smallpox (variola) on Aboriginal communities in Australia beginning in 1789 was catastrophic and continues to cause intergenerational trauma. Historically biased perspectives and contemporary misinformation of the disease's introduction and spread impede modern-day truth-telling and efforts towards reconciliation and national healing. Understanding whether the disease entered and spread from pre-colonial Makassan (Indonesian) trade along the northern coast, or from the British First Fleet's arrival in southeastern Australia in 1788, is necessary to estimate the demographic impact. Here we developed stochastic, multipatch epidemiological models supported by systematic evaluation of historical observations to test hypotheses regarding possible disease entry points, spread rate and demographic impacts. Our models support the hypothesis that entry of the disease was in southeastern Australia. Even under ideal conditions and with higher-than-probable infection rates, simulations show that smallpox was unlikely to reach Sydney from a northern entry. We found no evidence that the 1789 epidemic was Australia-wide. Assuming 60% lethality based on global data, the loss of approximately 220,000 people would have occurred in these regions. While catastrophic to traditional Indigenous lifeways in the southeast, the disease also provided the catalyst for population decline and marginalization of Indigenous people in the face of expanding European populations. Our models indicate that it is unlikely that other parts of Australia were affected by the initial epidemic. We warn readers that the content of this study might be distressing.