Laina Mercer

Pakistan is one of only three countries where poliovirus circula-
tion remains endemic. For the Pakistan Polio Eradication Program, identifying
high risk districts is essential to target interventions and allocate limited resources.
Methods: Using a hierarchical Bayesian framework we developed models to esti-
mate vaccination rates, population immunity, and a spatial Poisson hurdle model
to jointly model the probability of one or more paralytic polio cases, and the
number of cases that would be detected in the event of an outbreak. Rates of
underimmunization, routine immunization, and population immunity, as well as
seasonality and a history of cases were used to project future risk of cases. Results:
The expected number of cases in each district in a 6-month period was predicted
using indicators from the previous 6-months and the estimated coeclients from
the model. The model achieves an average of 90% predictive accuracy as measured
by area under the receiver operating characteristic (ROC) curve, for the past 3
years of cases. Conclusions: The risk of poliovirus has decreased dramatically in
many of the key reservoir areas in Pakistan. The results of this model have been
used to prioritize sub-national areas in Pakistan to receive additional immunization
activities, additional monitoring, or other special interventions.