Spatial model for risk prediction and sub-national prioritization to aid poliovirus eradication in Pakistan

Laina D. Mercer, Rana M. Safdar, Jamal Ahmed, Abdirahman Mahamud, M. Muzaffar Khan, Sue Gerber, Aiden O’Leary, Mike Ryan, Frank Salet, Steve J. Kroiss, Hil Lyons, Alexander Upfill-Brown, Guillaume Chabot-Couture

Pakistan is one of only three countries where poliovirus circulation remains endemic. For the Pakistan Polio Eradication Program, identifying high risk districts is essential to target interventions and allocate limited resources. Using a hierarchical Bayesian framework we developed 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. 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 coefficients 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. 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.