Evolution of the live-attenuated novel oral poliovirus type 2 (nOPV2) vaccine: detection of a double recombinant strain in Uganda

Uganda responded to a circulating vaccine derived poliovirus type 2 outbreak in August 2021 by deploying the novel oral polio vaccine type 2 (nOPV2), following its Emergency Use Listing authorization by the World Health Organization. Post-usage, three double recombinant sequences from virus isolates from one sewage specimen were obtained. These lacked the modified S15domV structure, the cis-acting replication element, and the amino acid substitutions in the viral RNA-dependent RNA polymerase, key features that were designed to make the novel oral polio vaccine type 2 more stable and these distinguish it from the monovalent oral polio vaccine type 2. While there has been no evidence of transmission of these recombinant viruses, their detection underscores the need for vigilant surveillance for early detection of such incidents and intensifying vaccination efforts to accelerate progress towards eradication.