About the Polio Endgame Strategic Plan
In May 2012 the World Health Assembly declared the completion of poliovirus eradication to be a programmatic emergency for global public health and called for a comprehensive polio endgame strategy. In response, the Polio Eradication and Endgame Strategic Plan 2013-2018 was developed.
The plan outlines a comprehensive approach for completing eradication including the elimination of all polio disease (both wild and vaccine-related).
As one of its four major objectives, the plan calls on countries to introduce at least 1 dose of Inactivated Polio Vaccine (IPV) into routine immunization schedules, strengthen routine immunization and withdraw Oral Polio Vaccine (OPV) in a phased manner, starting with type 2-containing OPV.
Why should countries introduce IPV?
Introducing IPV is a key element of the endgame plan and global readiness to manage risks associated with OPV type 2 withdrawal. The endgame plan calls for the introduction of IPV in all OPV-only using countries by the end of 2015. More specifically, IPV needs to be introduced for the following reasons:
• To reduce risks. Once OPV type 2 is withdrawn globally, IPV will help fill the immunity gap by priming population against type 2 polio virus should it be reintroduced. A region immunized with IPV would have a lower risk of re-emergence or reintroduction of wild or vaccine-derived type 2 polio virus.
• To interrupt transmission in the case of outbreaks. Should monovalent OPV type 2 (mOPV type 2) be needed to control an outbreak, those primed with IPV would be expected to have a better immune response, thus facilitating outbreak control and interruption of polio transmission.
• To hasten eradication. IPV will boost immunity against poliovirus types 1 and 3 in children who have previously received OPV, which could further hasten the eradication of these two wild viruses.
WHO Polio Position Paper, February 2014
A WHO Position Paper on polio vaccines published in February 2014 confirms that WHO no longer recommends an OPV-only vaccination schedule. For all countries using OPV only, at least 1 dose of IPV should be added to the schedule.
Why will countries need to switch from tOPV to bOPV?
There are three types of wild poliovirus (WPV) - type 1 (WPV1), type 2 (WPV2) and type 3 (WPV3) - each of which is targeted by a different component of the trivalent oral polio vaccine (tOPV).
Live attenuated vaccines are effective against the wild virus, but in very rare cases can lead to paralysis. There are two ways this can occur:
• Vaccine Associated Paralytic Poliomyelitis (VAPP): for every birth cohort of 1 million children in OPV-only using countries, there are 2-4 cases of VAPP. This translates to an estimated 250 – 500 VAPP cases globally per year. Of these, about 40% are caused by OPV’s type 2 component.
• Circulating Vaccine Derived Poliovirus (cVDPV) outbreaks: these rare outbreaks occur when a vaccine-related virus is passed from person-to-person, mutating along the way and acquiring wild virus transmissibility and neurovirulence characteristics. Almost all cVDPV outbreaks in recent years have been caused by a type 2 vaccine-derived virus.
The vast majority of cVDPV outbreaks and a substantial portion of the total VAPP cases are due to the type 2 component of OPV. Wild poliovirus type 2 appears to have been eradicated globally in 1999 and the risk of paralytic disease due to the type 2 component of OPV now outweighs its benefits. Thus, tOPV will be replaced with bivalent OPV (bOPV), which will continue to target the remaining polio types (WPV1 and WPV3). Once these types are eradicated, bOPV will also be withdrawn.