A novel tool to eradicate an ancient scourge: the novel oral polio vaccine type 2 story

The recent detection of vaccine-derived poliovirus (VDPV) in London (UK) and a case of paralytic polio in New York (USA) have highlighted how the scourge of poliomyelitis has not been totally overcome and remains an international problem, not confined to Afghanistan and Pakistan (where wild-type 1 poliovirus remains endemic) or as outbreaks of circulating VDPV in countries in Africa. To address the risk of circulating VDPVs, a global collaborative effort over the past decade has enabled the development of novel oral polio vaccine type 2 (nOPV2) that is as immunogenic as the current Sabin strain and so equally effective, while being less likely to revert to neurovirulence than Sabin oral polio vaccines. The successful development of nOPV2-the first such vaccine against type 2 poliovirus and the first vaccine ever authorised by the WHO Prequalification team through its Emergency Use Listing procedure-has led to the deployment of approximately 450 million doses of nOPV2 for outbreak control in 21 countries. It also paved the way for the subsequent Emergency Use Listing approval of COVID-19 vaccines in the global pandemic. Monitoring the use of nOPV2 has confirmed it is more genetically stable and less likely to result in VDPV than the Sabin strain, suggesting that the target of the global eradication of poliomyelitis might be a little more attainable than previously believed.