While 3 wild poliovirus strains—types 1, 2, and 3—have caused worldwide disease, type 2 has not been detected since 1999, and with its elimination confirmed in September 2015, the need to vaccinate against it has abated. In April more than 150 countries and territories switched from using the trivalent oral poliovirus vaccine (OPV), which protects against the 3 strains of wild poliovirus, to the bivalent OPV, which lacks the type 2 strain (http://bit.ly/1SIFoua). These oral vaccines are made with live attenuated polioviruses.
Friedrich MJ. Switch From Trivalent to Bivalent Oral Polio Vaccine. JAMA. 2016;315(23):2513. doi:10.1001/jama.2016.6686