OPV, given orally, provides protection in the mouth, intestines (where they multiply), and subsequently, the blood. IPV, given through intramuscular injection, provides protection in the blood and enhances the protection given by the OPV against polio.
For the IPV, the currently published DOH NIP schedule indicated only one dose to be given together with the 3rd dose of OPV at 3 1/2 months. Additionally, if this dose was missed, it must be given as soon as possible before the infant turns a year old.
However, more recently, to protect the infants from polio outbreak due to low immunization rates brought about by the pandemic, a booster dose is given during infancy at 9 months or at least 6 months from the previous IPV dose.
For your reference on IPV, please see links here: