Genetic characterization of novel oral polio vaccine type 2 viruses during initial use phase under emergency use listing--worldwide, March-October 2021/Caracterisation genetique des virus issus du nouveau vaccin antipoliomyelitique oral de type 2 pendant la phase initiale d'utilisation d'urgence au titre du protocole EUL--dans le monde, mars-octobre 2021.

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From: Weekly Epidemiological Record(Vol. 97, Issue 26)
Publisher: World Health Organization
Document Type: Article
Length: 5,061 words
Lexile Measure: 2010L

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The emergence and international spread of neurovirulent circulating vaccine-derived polioviruses (cVDPVs) throughout many countries in Africa and Asia in recent years pose a major challenge to the goal of eradicating all forms of poliovirus. Approximately 90% of all cVDPV outbreaks are caused by the type 2 strain of the Sabin vaccine, an oral live, attenuated vaccine; cVDPV outbreaks typically occur in areas of persistently low immunization coverage. (1) A novel type 2 oral poliovirus vaccine (nOPV2), produced by genetic modification of the type 2 Sabin vaccine virus genome, (2) was developed and evaluated in phase I and phase II clinical trials during 2017-2019 and was demonstrated to be safe and well-tolerated, have noninferior immunogenicity, have better genetic stability than Sabin monovalent type 2 (as measured by preservation of the primary attenuation site [domain V in the 5' noncoding region] and show significantly less neurovirulence of faecally shed vaccine virus in transgenic mice). (3,4,5) These findings indicate that nOPV2 could be important for reducing the risks of generating VDPVs and of vaccine-associated paralytic poliomyelitis. In view of the favourable preclinical and clinical data and the public health emergency of international concern represented by ongoing endemic wild poliovirus transmission and cVDPV type 2 outbreaks, WHO authorized nOPV2 for use under the emergency use listing (EUL) pathway in November 2020, permitting its first use for outbreak response in March 2021. (6) As required in the EUL obligations, an extensive plan was developed and followed for obtaining and monitoring nOPV2 isolates detected during acute flaccid paralysis (AFP) surveillance, environmental surveillance, adverse events after immunization surveillance and targeted surveillance for adverse events of special interest (i.e., prespecified events that could be causally associated with the vaccine product), during outbreak response and in planned field studies. In this monitoring framework, data generated from whole-genome sequencing of nOPV2 isolates and other virological data on isolates from AFP and environmental surveillance systems are reviewed by the genetic characterization subgroup of an nOPV working group of the Global Polio Eradication Initiative. Global nOPV2 genomic surveillance during March-October 2021 confirmed the genetic stability of the primary attenuating site. Sequence data generated in this unprecedented global work confirm the genetic stability of nOPV2 relative to Sabin 2 and suggest that nOPV2 will be important in the eradication of poliomyelitis. nOPV2 surveillance should continue for the duration of the EUL.

Approximately 111 million doses of nOPV2 were administered worldwide during the initial use phase (March-October 2021). During this period, 128 nOPV2 isolates were detected from stool specimens collected as part of routine AFP surveillance in 6 countries, and 123 nOPV2 isolates corresponding to 39 distinct environmental surveillance samples were detected in 7 countries. Whole-genome sequences were generated for these 251 nOPV2 cell-culture isolates. (7) The intervals between nOPV2 supplementary immunization activity (SIA) and sample collection ranged from 0 to 81 days for AFP samples (mean = 12.5 days; median = 7 days) and from 4 to 67 days for environmental surveillance samples (mean = 22.8; median = 16). The sequence of each...

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Gale Document Number: GALE|A709814537