. 2017 Jul 1;216(Suppl 1):S9–S14. doi: 10.1093/infdis/jiw592

Table 1.

Summary Definitions of Risk Tiers for IPV Introduction Based on Risk of cVDPV2 Outbreaks and Importations After Cessation of the Type 2 Component of OPV

Tier	Definition
Tier 1	WPV-endemic countries or countries that have reported a cVDPV2 since 2000
Tier 2	Countries that have reported a cVDPV1/cVDPV3 since 2000 or large/medium-sized^a countries with DTP3 vaccine coverage of <80% in 2012, 2013, or 2014, according to WUENIC
Tier 3	Large/medium-sized^a countries adjacent to tier 1 countries that reported WPV since 2003 or countries that have experienced a WPV importation since 2011
Tier 4	All other countries using OPV

Abbreviations: cVDPV1, cVDPV2, and cVDPV3, circulating vaccine-derived poliovirus types 1, 2, and 3, respectively; DTP3, third dose of the diphtheria-tetanus-pertussis vaccine; IPV, inactivated poliovirus vaccine; OPV, oral poliovirus vaccine; WPV, wild poliovirus; WUENIC, World Health Organization/United Nations Children’s Fund Estimates of National Immunization Coverage.

^aSmall, medium-sized, and large countries were defined as those with <20 000, 20000 to 1 million, or >1 million live births, respectively.