Joel Miller

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  Role of vaccination in determining the critical community size for stochastic extinction
  Joel Miller
  A recent localized outbreak of CVDPV-2 (circulating vaccine-derived Polio virus 2) in Syria caused great concern for the ongoing effort to eradicate Polio. Over 70 children experienced symptoms in a relatively localized geographic region. Given the fact that fewer than 1 in 1000 infected children would be expected to experience symptoms, this suggests a very high attack rate in the region. No cases have been identified since September, and there is (as yet) no evidence that it has spread from the region. A plausible explanation is that lack of vaccination in the region led to a large outbreak which then went extinct, hopefully without seeding other regions. This leads to the possibility that there may be two modes for extinction in a sufficiently isolated community: either high vaccination leading to high immunity, or a large epidemic leading to high immunity. It is plausible that there is an intermediate regime where insufficient vaccination coverage leads to persistence within a community. I will use simulation and analytic models to explore this further. This work is very preliminary and should be interpreted as a speculative attempt to explore scenarios.