Duelling timescales of host mixing and disease spread determine invasion of disease in structured populations

The epidemic potential of a disease is traditionally assessed using the basic reproductive number, R₀. However, in populations with social or spatial structure a chronic disease is more likely to invade than an acute disease with the same R₀, because it persists longer within each group and allows for more host movement between groups. Acute diseases ‘perceive’ a more structured host population, and it is more important to consider host population structure in analyses of these diseases. The probability of a pandemic does not arise independently from characteristics of either the host or disease, but rather from the interaction of host movement and disease recovery timescales. The R_* statistic, a group-level equivalent of R₀, is a better indicator of disease invasion in structured populations than the individual-level R₀.