Why OPV cessation?
Oral polio vaccine (OPV) is extremely safe and effective at protecting children against lifelong polio paralysis. Over the past ten years, more than 10 billion doses of OPV have been given to nearly three billion children worldwide. More than 10 million cases of polio have been prevented, and the disease has been reduced by more than 99%. It is the appropriate vaccine through which to achieve global polio eradication.
OPV contains attenuated (weakened) polioviruses. On extremely rare occasions, use of OPV can result in cases of polio due to vaccine-associated paralytic polio (VAPP) and circulating vaccine-derived polioviruses (cVDPVs). For this reason, the global eradication of polio requires the cessation of all OPV in routine immunization, as soon as possible after the eradication of wild poliovirus (WPV) transmission.
Phased approach to OPV cessation – trivalent OPV to bivalent OPV switch
OPV is available in different formulations:
· Trivalent OPV – containing type 1, 2 and 3 serotypes
· Bivalent OPV – containing type 1 and 3 serotypes
· Monovalent OPV – containing one serotype (ie type 1, 2 or 3)
A mix of all formulations is used to eradicate polio during supplementary immunization activities (SIAs). Trivalent OPV is the only formulation used in routine immunization programmes. Bivalent OPV is the most widely-used formulation during SIAs to more rapidly interrupt the remaining strains of WPV1 and 3 transmission – the only remaining WPV strains in circulation. WPV2 has been eradicated since 1999.
With WPV2 transmission already having been successfully interrupted, the only cases of paralytic polio now are caused by the type 2 serotype component in trivalent OPV. Over 90% of cVDPV cases are due to the type 2 component, which is also responsible for up to 38% of VAPP cases. See cVDPV updates
That is why a switch will be implemented from trivalent OPV to bivalent OPV in routine immunization programmes, even before the remaining strains of WPV1 and WPV3 transmission are eradicated.
Following WPV1 and WPV3 eradication, use of all OPV in routine immunizations will subsequently be stopped.
A switch from trivalent OPV to bivalent OPV will be associated with significant public health benefits. More 90% of all cVDPV cases, currently caused by the type 2 component of trivalent OPV, and up to 38% of all VAPP cases, would no longer occur.
In addition to these significant humanitarian benefits, OPV type 2 cessation would provide the GPEI with a 'push' for global OPV cessation of all OPVs. Feasibility of OPV cessation would be underscored in practice, and would ensure a 'trial run' for all OPV cessation. Key lessons would be learnt to ensure that this process can be implemented in the safest and most efficient manner.
Programmatic implications of trivalent OPV to bivalent OPV switch
To minimise the risks associated with the phased removal of OPV, countries must adequately prepare for an eventual trivalent OPV to bivalent OPV switch (followed by the cessation of all OPVs altogether). The primary risk associated with such a switch will be the increase in susceptible populations to poliovirus type 2, which in turn would increase the risk of new cVDPV type 2 emergence in the immediate period following OPV type 2 cessation. Safely managing these risks will be key to a successful switch from trivalent to bivalent OPV.
Inactivated polio vaccine (IPV):
To maintain immunity levels to type 2 polio, all countries should introduce at least one dose of IPV into routine immunization programmes prior to – or at the time of – an eventual switch. IPV will at that point be the only vaccine with which to maintain immunity to type 2 polio.
Access to bivalent OPV in routine immunization:
Bivalent OPV is currently licensed for use during SIAs only. Access to sufficient supplies of bivalent OPV licensed for routine immunization use will need to be available.
Maintaining outbreak response capacity:
At the same time, outbreak response capacity will have to be maintained, including ensuring the supply and management of stockpiles of appropriate type 2-containing vaccines to facilitate an appropriate outbreak response should it be necessary.
All WPV2 and Sabin type 2 viruses must be placed under appropriate biocontainment levels on a timely basis to minimise the risk of re-introduction into a type 2 polio-free world.
Verification of WPV2 eradication:
The Global Commission for the Certification of the Eradication of Poliomyelitis (GCC) will review data from all six WHO regions to determine whether there is sufficient evidence to conclude formally that WPV2 has been eradicated globally.
The trigger for setting a definitive date for the withdrawal of the type 2 component of the oral polio vaccine globally will be the absence of all persistent cVDPV2 for at least six months.
More information on OPV cessation and IPV introduction
The Global Polio Eradication Initiative © Copyright 2010