The widespread use of trivalent Oral Poliomyelitis Vaccine (tOPV), coupled with targeted campaigns using monovalent OPV (mOPV), has proven to be an effective tool in combating wild poliovirus and can be credited to date with the interruption of transmission of wild poliovirus in all but 4 countries in the world. This represents more than a 95 percent reduction in polio-endemic countries worldwide since the signing of the World Health Assembly resolution in 1988, through which all member nations pledged to eradicate polio.  

Read on below, consult frequently asked questions on OPV cessation or read about research into options for safely stopping OPV use.

Despite the safety and effectiveness of OPV, the live attenuated vaccine virus causes vaccine-associated paralytic poliomyelitis (VAPP) at a rate of 1 case per 750 000 to 1 million children receiving their first dose of OPV [i],[ii].  While the public health benefits of OPV continue to outweigh the VAPP risk in most countries[iii], this balance will change with the interruption of wild poliovirus transmission in all countries.  An estimated 250-500 cases of VAPP would continue to occur each year in OPV-using countries based on current utilization patterns[iv]. 

In addition to the problem of VAPP in a 'polio-free' world, OPV viruses under some circumstances regain both neurovirulence and the capacity to circulate [v].  Such circulating vaccine-derived polioviruses (cVDPVs) have been established as the source of polio outbreaks that paralyzed people in up to six different countries over the last five years.

In recognition of these risks, a WHO consultation on the subject of VAPP and VDPVs concluded in 2003 that routine use of OPV must be discontinued in the post-eradication era.  This later became one of the recommendations of the Advisory Committee on Poliomyelitis Eradication (ACPE), which confirmed that VDPVs pose a major threat to the global goal of eliminating paralysis induced by circulating polioviruses and as long as OPV is used, particularly in areas of low immunization coverage, this threat would persist.

The epdiomological risks associated with stopping all tOPV use in routine immunization can be divided into two categories: 

1. the immediate risk of cVDPV emergence

2. the long-term risk of inadvertent poliovirus re-introduction. 

As countries stop using OPV, there will be an immediate risk of cVDPV emergence which would require an outbreak response.  Mathematical models suggest that even with simultaneous cessation of OPV use worldwide there is a 65-90% chance of at least one such outbreak somewhere in the world during the 12 months immediately after cessation, with that risk declining to 1-5% at 36 months[xii].  Countries with low routine immunization coverage at the time of OPV cessation are expected to be at greatest risk.  After stopping OPV and in the long-term thereafter, there remains the risk of re-introducing a wild, vaccine-derived or Sabin poliovirus strain from a vaccine production site, a laboratory or an iVPDV.  

The magnitude of poliovirus facility-associated risks is largely contingent on the extent of poliovirus destruction and quality of global poliovirus 'containment' activities.  The principle dimensions of this risk concern the thoroughness of searches for risk materials, how their destruction takes place and how viruses themselves will be handled.  

Protective measures will concentrate on both the safety of workers and the minimization of any chance that infectious materials could leave a given facility.  An inadvertent release of any virus into a polio-free world could have grave consequences, particularly for countries which stop all polio immunization and therefore would have a highly susceptible population. 

It should also be noted that there will be significant programmatic challenges that threaten an effective cessation of OPV.  Before any change of policy can be implemented, a global consensus must be reached on the need to stop using OPV.  The international bodies providing oversight to the Global Polio Eradication Initiative have already endorsed the need for eventual simultaneous OPV cessation. A World Health Assembly Resolution will also be needed confirming international agreement on this issue.

In addition, it will be necessary to ensure that no country is inadvertently put at risk of importing a cVDPV from a country that continues to use OPV. For this reason, the cessation of OPV must occur in a simultaneous manner, world-wide.

The strategies needed to minimize and manage the risks associated with eventual OPV cessation are considered 'prerequisites' for stopping routine immunization with this vaccine. The six prerequisites that have been established by the Polio Eradication Initative for OPV cessation are as follows.  

1. Confirmation of interruption of wild poliovirus transmission and appropriate containment
2. Continued highly sensitive surveillance for poliovirus circulation
3. Development of an international stockpile of mOPV and response mechanisms
4. Implementation of IPV requirements in bio-hazard settings
5. International consensus on procedure for synchronous OPV cessation
6. Appropriate biocontainment of Sabin polioviruses

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