Polio vaccine given outside the United States is valid if written documentation indicates that all doses were given after 6 weeks of age and the vaccine received was IPV or trivalent OPV (tOPV). Only trivalent polio vaccine counts toward the U.S. schedule. No doses of OPV given since April 1, 2016, count toward the U.S. polio vaccination schedule because, on that date, all countries routinely using tOPV switched to bivalent OPV. Please see other detailed answers concerning details on assessment of OPV doses by the date of administration.
If both tOPV and IPV were or will be administered as part of a series, the total number of doses needed to complete the series is the same as that recommended for the U.S. IPV schedule. If the child is younger than 4 years of age a total of 4 doses of polio vaccine are recommended. If the child is currently 4 years of age or older, a total of 3 doses completes the series. A minimum interval of 4 weeks should separate doses in the series, with the final dose administered on or after the fourth birthday and at least 6 months after the previous dose. If only tOPV was administered, and all doses were given before 4 years of age, 1 dose of IPV should be given at 4 years of age or older, at least 6 months after the last tOPV dose.