By Ethan Covey
Circulating vaccine-derived poliovirus (cVDPV) outbreaks, which can occur in underimmunized groups, occurred in 37 countries during 2020, and global cases increased from 366 in 2019 to 1,078 in 2020.
Most cases (86%) were caused by cVDPV type 2, affecting 28 African countries (MMWR Morb Mortal Wkly Rep 2021;70:1691-1699).