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Owing to the concerted efforts of countries worldwide, the incidence of paralytic poliomyelitis due to wild poliovirus infection has been reduced to its lowest on record. Wild poliovirus type 2 has not been detected since 1999 and was certified to have been eradicated in 2015. No case of paralytic poliomyelitis caused by wild poliovirus type 3 has been reported since 2012, and all cases detected since 2013 have been due to wild poliovirus type 1. In 2016, only 37 cases of paralytic poliomyelitis caused by wild poliovirus infection were reported, and that number decreased to 22 in 2017. Global eradication of wild poliovirus—the long-awaited outcome of decades of effort—is finally in sight. However, roughly 300–500 cases of vaccine-associated paralytic poliomyelitis (VAPP) each year are caused by the oral poliovirus vaccine (OPV), meaning that cases of paralytic poliomyelitis caused by vaccination now exceed cases caused by wild poliovirus infection. Paradoxically, vaccination has become the main source of polio paralysis in the world. To eliminate VAPP and its negative social impact, WHO plans to withdraw all OPVs and to implement a change to use of inactivated poliovirus vaccine (IPV). However, this change can only occur after global eradication of wild poliovirus has been certified, which will be at least 3 years after the last case of wild poliovirus infection. Even if the two most recent cases, which occurred on Feb 19, 2018, in Afghanistan, are the last in the world, global eradication of wild poliovirus will be no sooner than 2021–22; thus, OPV will not be withdrawn until 2022–23. As an interim measure, and under the favourable conditions of low numbers of wild poliovirus infections, on May 1, 2016, 155 countries using OPV in their immunisation programmes switched from use of trivalent OPV (types 1, 2, and 3) to use of bivalent OPV (types 1 and 3). This switch is expected to eliminate VAPP induced by poliovirus type 2 and circulating vaccinederived poliovirus type 2. Circulating vaccine-derived poliovirus is an attenuated virus that has regained neurovirulence and can transmit from person to person, causing outbreaks of paralytic poliomyelitis. Circulating vaccine-derived polio virus type 2 contributed to 92% (365/395) of all reported cases of infections caused by circulating vaccine-derived polioviruses in 2011–17. It was also decided by WHO that at least one injection of IPV, which contains all three types of inactivated poliovirus, should be included in the immunisation programmes of OPV-using countries to protect against possible outbreaks of poliovirus type 2 in the future. The main challenge to the new plan is the availability of IPV. Because of insufficient production capacity, many countries have a severe shortage of these vaccines. For example, in China, we estimated from official data that the market gap in 2016 for IPV was about 5·96 million doses or 32·3% of need. Even if the rapid expansion of production in China goes to plan, with targets being met in early 2018, the IPV shortage in other countries will be difficult to remedy in the short term. Implementation of the new plan has increased public expectation of the safety of bivalent OPV and has reduced tolerance of VAPP risk. In an on-going study (unpublished) of patients with VAPP in China, we observed five new cases of VAPP between July and September, 2016. All five cases were due to administration of bivalent OPV as the first dose because of an IPV shortage. These cases resulted in temporary social panic in some provinces and increased concerns about the new programme. Although bivalent OPV is thought to be safer than the trivalent vaccine and has been widely used for many years in supplemental immunisation activities, it has been used in smaller areas and less frequently than trivalent OPV. Research on the safety of bivalent OPV alone is scarce. However, a study in Beijing showed that no VAPP occured during the 7 months of administration of IPV followed by bivalent OPV from April to December, 2016. Because of the delay in and incomplete disclosure of information from the adverse events following immunization (AEFI) monitoring system, we cannot yet establish whether the number of VAPPs has decreased nationally and globally as expected. Given that bivalent OPV must continue to be widely used until 2022–23, new VAPP cases are inevitable. At such a sensitive time, further reduction of the occurrence of VAPP is crucial. In this Viewpoint, we discuss two important issues of poliovirus vaccination: the sequence and timing of vaccinations and the screening of contraindications before vaccination. The relative risk of VAPP with different doses of OPV needs to be clarified. For all countries using OPV, WHO suggests administration of multiple doses of bivalent OPV and at least one dose of IPV. However, in countries with high vaccination coverage (eg, 90–95%) and low risk of poliovirus importation (ie, neighbouring countries and major population movement all having similarly high coverage), the suggested sequence is one or two doses of IPV followed by at least two doses of bivalent OPV. By contrast, in polio-endemic countries and countries with lower vaccination coverage and high Published Online March 28, 2018 http://dx.doi.org/10.1016/ S0140-6736(18)30483-5