In a few countries, ID was originally the standard route of delivery for inactivated poliovirus vaccine, but injection depth was later shifted to IM (Weniger and Papania 2008) . Studies have found that ID delivery of reduced doses is capable of inducing seroconversion, which may help make this vaccine more affordable for use in developing countries (Samuel et al. 1991; Samuel et al. 1992; Nirmal et al. 1998 ). More recently, the WHO Global Polio Eradication Initiative has worked to determine the potential for this mode of delivery to be used in post-eradication settings after phase-out of oral polio vaccine.