The Endgame for Elimination of Polioviruses

Abstract Since the Global Polio Eradication Initiative (GPEI) was launched in 1988, the number of polio‐endemic countries has declined from 125 to 3 (Afghanistan, Pakistan and Nigeria) in 2016, with a 99% reduction in polio cases globally. In 2017, only 22 cases from two countries, Afghanistan and Pakistan, were reported compared to 37 cases in 2016. This remarkable progress has been attributed to internationally coordinated public health efforts led by national governments in partnership with GPEI through increased accountability, utilisation of new technologies and particularly implementation of four core strategies. These strategies include achieving and maintaining high coverage rates through routine immunisation with oral and inactivated polio vaccines (OPV and IPV); providing supplementary doses of vaccines through mass campaigns; surveillance of children with acute flaccid paralysis (AFP) and conducting targeted ‘mop‐up’ campaigns with vaccines. In 2013, GPEI outlined a path to securing eradication through the Polio Eradication and Endgame Strategic Plan 2013–2018 (PEESP). The PEESP's four main objectives include: (1) detection and interruption of poliovirus; (2) strengthening of immunisation systems and withdrawal of OPV; (3) containment and certification and (4) responsible transition of polio resources, infrastructure and lessons learned. As we reach the final chapter of polio eradication, a lot of work remains to be done to ensure the successful eradication of polio. As the virus continues to circulate in high‐risk areas of Afghanistan, Pakistan and Nigeria, there is a real threat to countries with less‐than‐adequate immunisation coverage and weak AFP surveillance systems. Now more than ever, achieving high immunisation coverage and maintaining high‐quality surveillance are critical to ensure that population immunity remains strong and that any emerging cases are identified and responded to immediately. Key Concepts Polio is about to become the second human disease to be eradicated after smallpox. By 2016, only 37 cases of polio caused by wild polioviruses were reported in three countries, Pakistan, Afghanistan and Nigeria, which is a more than 99% decrease from an estimated >350 000 cases worldwide in 1988. Much of the remarkable progress made in polio eradication has been mainly due to widespread use of vaccines, combined with improved surveillance of children with acute flaccid paralysis. Two different types of vaccine are available, an inactivated polio vaccine (IPV) and the live‐attenuated oral polio vaccine (OPV) with OPV being the major vaccine type used to achieve eradication and IPV being critical to sustain eradication. With the acknowledgement of previously missed target dates for polio eradication, the Polio Eradication and Endgame Strategic Plan 2013–2018 (PEESP) was developed to outline a path to securing eradication. Very rarely, the attenuated vaccine virus in OPV may revert to a genetically unstable variant which may enter the central nervous system and cause a polio‐like illness known as vaccine‐associated paralytic poliomyelitis (VAPP). Circulating vaccine‐derived polioviruses (cVDPVs) which occur very rarely can also cause outbreaks of polio. These are vaccine viruses, which through prolonged transmission from susceptible to susceptible lead to mutations, which results in vaccine viruses with the transmissibility and neurovirulence properties of wild viruses. Eradicating polio completely from the world will involve elimination of both wild and vaccine‐derived polioviruses (VAPP and VDPVs). OPV cannot be used indefinitely and will be discontinued completely in immunisation programmes after successful interruption of WPV transmission. The global cooperation, political will and partnerships leveraged for polio eradication serve as an example of what is possible when a global community works together to achieve a common goal.