Super-spreading occurs when individual variation in infectiousness leads to a small fraction of cases causing most transmission.
Dispersion Parameter (k)
- k < 1: Highly overdispersed (super-spreading)
- k = 1: Geometric distribution
- k → ∞: Homogeneous (Poisson)
- COVID-19: k ≈ 0.1-0.5
The 20/80 Rule
- ~20% of cases cause ~80% of transmission
- Most infected people infect no one
- Outbreaks driven by rare super-spreading events
Implications
Low k means higher probability of stochastic extinction but also risk of explosive outbreaks from single events.