Top 5 Takeaways

  1. Novel OPV2 Shows Genetic Stability: Global genomic surveillance confirms the genetic stability of the novel oral poliovirus vaccine type 2 (nOPV2), maintaining the primary attenuating site’s integrity during its initial use phase.
  2. Widespread Use and Monitoring: Approximately 111 million doses of nOPV2 were administered worldwide, with 251 isolates analyzed from AFP and environmental surveillance, demonstrating mostly unchanged genetic profiles compared to the vaccine strain.
  3. Reduced Neurovirulence and Vaccine-derived Poliovirus Risks: nOPV2 is designed to mitigate the risks associated with traditional Sabin OPVs, including the emergence of vaccine-derived polioviruses (VDPVs) and vaccine-associated paralytic poliomyelitis.
  4. Monitoring Reveals No Significant Reversions: No significant reversions in the primary attenuation site were observed across the analyzed isolates, suggesting a low risk of nOPV2 contributing to new VDPV outbreaks.
  5. Continued Surveillance Recommended: Despite encouraging initial results, ongoing surveillance and analysis are necessary to ensure the long-term efficacy and safety of nOPV2 in poliovirus eradication efforts.

Original Article Author and Citation

Corresponding Author

Cara C. Burns,

Suggested Citation

Martin J, Burns CC, Jorba J, et al. Genetic Characterization of Novel Oral Polio Vaccine Type 2 Viruses During Initial Use Phase Under Emergency Use Listing — Worldwide, March–October 2021. MMWR Morb Mortal Wkly Rep 2022;71:786–790. DOI:


This MMWR article provides a comprehensive overview of the genetic characterization of nOPV2 during its initial use phase under the WHO’s Emergency Use Listing. It highlights the global effort to monitor the genetic stability of nOPV2, a genetically modified vaccine designed to prevent poliovirus outbreaks with lower risks of generating new circulating vaccine-derived polioviruses (cVDPVs).


The study involved the global genomic surveillance of nOPV2 isolates obtained from stool specimens collected as part of routine acute flaccid paralysis (AFP) surveillance, environmental surveillance, and during outbreak responses. Whole-genome sequencing was used to analyze the genetic stability of these isolates compared to the nOPV2 vaccine strain.


The findings confirm the genetic stability of nOPV2, with the majority of isolates showing no significant genetic drift from the vaccine strain. The article discusses the implications of these results for poliovirus eradication efforts, emphasizing the importance of continued surveillance to monitor for potential genetic changes that could impact vaccine efficacy and safety.


The initial use phase of nOPV2 under the Emergency Use Listing has demonstrated promising results in terms of genetic stability and safety. The continuation of rigorous global surveillance is crucial for ensuring the success of polio eradication initiatives and the long-term effectiveness of nOPV2.

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