The Potential Impact of Routine Immunization with Inactivated Poliovirus Vaccine on Wild-type or Vaccine-derived Poliovirus Outbreaks in a Posteradication Setting

The "endgame" for worldwide poliomyelitis eradication will entail eventual cessation of the use of oral poliovirus vaccine (OPV) in all countries to prevent the reintroduction of vaccine-derived polioviruses--exposing some populations to an unprecedented, albeit low, risk of poliovirus outbreaks. Inactivated poliovirus vaccine (IPV) is likely to play a large part in post--OPV management of poliovirus risks by reducing the consequences of any reintroduction of poliovirus. In this article, we examine the impact IPV would have on an outbreak in a partially susceptible population after OPV cessation, using a mathematical model of poliovirus transmission with a realistic natural history and case reporting. We explore a range of assumptions about the impact of IPV on an individual's infectiousness, given the lack of knowledge about this parameter. We show that routine use of IPV is beneficial under most conditions, increasing the chance of fadeout and reducing the expected prevalence of infection at the time of detection. The duration of "silent" poliovirus circulation prior to detection lengthens with increasing coverage of IPV, although this only increases the expected prevalence of infection at the time of the OPV response if IPV has a very limited impact on infectiousness. Overall, the model predicts that routine use of IPV will be advantageous for the posteradication management of poliovirus.