OPV Cessation
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 20 billion doses of OPV have been given to nearly three billion children worldwide. More than 20 million cases of polio have been prevented, and the disease has been reduced by more than 99%.
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
Historically, OPV has been 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 three formulations was being used to eradicate polio during supplementary immunization activities (SIAs). However, only trivalent OPV was used in routine immunization programmes. Bivalent OPV was exclusively used during SIAs to more rapidly interrupt the transmission of WPV1 and 3 – the only remaining WPV strains in circulation. WPV2 has been eradicated since 1999.
With the transmission of WPV2 already successfully interrupted, the only cases of type 2 paralytic polio were being caused by the type 2 serotype component in trivalent OPV. Over 90% of cVDPV cases were due to the type 2 component, which was also responsible for up to 38% of VAPP cases (approx. 200 cases per year worldwide).
The switch
In April 2016 a switch was implemented from trivalent OPV to bivalent OPV in routine immunization programmes. Following WPV1 and WPV3 eradication, use of all OPV in routine immunizations will be stopped.
The Switch Evaluation and Report – current status and next steps (as at July 2024)
In 2023, the GPEI commissioned an evaluation of the 2016 global switch from use of trivalent OPV to bivalent OPV from routine immunization programmes, to inform both current strategies for most effectively stopping polio transmission and future polio vaccine cessation efforts.
Throughout 2024, the evaluation underwent extensive peer and stakeholder review and input, including through publication of a draft for public consultation, and ongoing advice and guidance from such groups as the World Health Assembly, the Strategic Advisory Group of Experts on immunization (SAGE), the Independent Monitoring Board (IMB), and other global and regional policy and advisory bodies. This procedure is in line with other WHO reviews and publications, to ensure full and comprehensive review.
As expected, the evaluation highlighted a number of shortcomings of the switch implementation, and these insights will help improve the planning for the eventual cessation of all OPV use, anticipated to occur after the successful global certification of wild poliovirus (WPV) eradication. The evaluation is expected to help inform the SAGE’s deliberations into broader post-certification strategic planning, when the group next meets in September, and will ultimately culminate in strengthened measures to more effectively secure a lasting polio-free world.
The GPEI welcomes this expert evaluation, and similar ongoing evaluations and guidance on all aspects of the polio eradication effort, to ensure that collectively the world can rapidly achieve a lasting polio-free world in the most rapid and effective manner possible.
The programme recognizes the serious ongoing threat posed by any poliovirus – be it wild- or variant poliovirus—every child paralyzed by polio is one child too many. The GPEI leadership continues to engage closely with affected countries to ensure leaders are committed to prioritizing reaching every remaining un- or under-immunized child, including through both supplementary immunization activities and strengthened routine immunization.
The final report of the switch evaluation will be published at this location once the review process has been completed, anticipated to occur following the next SAGE meeting in September 2024.
