Oral polio vaccine risks and eradication

Risks related to opv vaccine and its consequences

1. OPV Risks: VAPP, chronic infection, genetic reversion, VDPV emergence, circulation, and exportation. Polio outbreaks from circulating VDPVs. Risk-Benefit Dynamics: Initially, risks were small compared to natural polio incidence. As natural polio declined, risks outweighed benefits. WPV-2 Eradication (1999): Removal of type 2 vaccine virus in OPV post-WPV-2 eradication. “OPV Risks and Consequences: A Critical Assessment"

2. Errors and Complications: Absence of a time-bound plan to replace OPV with IPV. International experts delaying the switch to IPV until wild polioviruses and cVDPVs are eradicated. Scientific Incompatibility: Any use of OPV seems incompatible with polio eradication. IPV Significance: In a polio-eradicated world, only IPV is viable. The potential of IPV to expedite the eradication Endgame is underestimated.

3. Polio Endgame Till 2014: Exclusive use of trivalent OPV (tOPV) as the primary tool for polio eradication targets. Efficacy Concerns from India (1970s): Studies from India in the 1970s highlighted the low efficacy of tOPV. Reports indicated failure to provide protection against polio despite administering three doses of tOPV.

4. Type 2 Eradication (Pre-2000): Successful eradication of type 2 before 2000. Continued Use of tOPV with Type 2: tOPV, including type 2 vaccine virus, administered until the global switch in 2016. Emergence of VDPVs and cVDPV-2 Outbreaks: Type 2 vaccine virus led to the emergence of VDPVs. cVDPV-2 caused multiple outbreaks globally. Response and Consequences: To control cVDPV-2 outbreaks, monovalent OPV type 2 used in campaign mode. This strategy contributed to the emergence of more cVDPV lineages.

5. VAPP, a rare adverse effect of OPV, is more linked to type 3 vaccine virus. This underscores the potential for attenuated vaccine virus, like wild poliovirus, to regain neurovirulence and cause paralysis in vaccine recipients by invading the spinal cord. Global safety concerns led to replacing OPV with IPV, licensed earlier in the West. IPV, highly effective and without serious adverse effects (3 doses plus a booster), replaced OPV.

6. Affluent regions abandoned OPV by 2000 due to safety concerns, remaining polio-free. Notably, 3 doses of IPV are roughly as effective as 30 doses of OPV in many low-income tropical countries. A safer novel OPV vaccine type 2 (nOPV-2) was created to prevent genetic reversion. Unfortunately, widespread use in African countries resulted in nOPV-2 evolving into cVDPV2, causing polio outbreaks in Africa.

7. Polio epidemiology, with a low median age, cases in exclusively breastfed infants, and no waterborne outbreaks, suggests a respiratory transmission route. This challenges the belief in OPV's necessity for local intestinal immunity, lacking evidence support. In 2022, cVDPV-2 polio was detected in the USA in an unvaccinated adult, spreading widely in New York due to a dip in local immunization coverage during the pandemic. Despite the USA switching from OPV to IPV in 2000, the virus circulated until coverage improved in 2022. Similar situations occurred in the UK. The respiratory transmission route was evident, as there was no fecal-oral contamination of water supplies. In India, except for urban slums, infant feeds rarely have fecal contamination. Reevaluating Polio Epidemiology: Implications for Transmission Routes and OPV Necessity"

8. India faced persistent challenges with polio from WPV types 1 and 3 during the Endgame periods. Despite interrupting WPV-2 transmission in 1999, the low efficacy of tOPV against types 1 and 3 hindered eradication. Continuing with tOPV, India couldn't successfully interrupt transmission of WPV-1 and 3 in 2010/2011. With monovalent OPV-1 (mOPV-1) and mOPV-3 showing significantly higher efficacy than trivalent OPV, India introduced them in 2006. This led to the successful interruption of WPV-3 in 2010 and WPV-1 in 2011, eventually declaring India polio-free in 2014. National Perspective: India's Struggle with Polio: Challenges Beyond WPV-2 Eradication"

9. With monovalent OPV-1 (mOPV-1) and mOPV-3 showing significantly higher efficacy than trivalent OPV, India introduced them in 2006. This led to the successful interruption of WPV-3 in 2010 and WPV-1 in 2011, eventually declaring India polio-free in 2014. India's triumph in WPV elimination resulted from Health Ministry efforts and community support, achieving near-100% mOPV coverage through pulse polio campaigns. In 2016, India complied with WHO, adopting two fractional IPV doses at 6 and 14 weeks and switching to bOPV. A recent addition includes another fractional IPV dose at 9 months of age.

10. The Indian Academy of Pediatrics recommends IPV-containing vaccines for three primary doses and booster shots at specific intervals. The National Immunization Schedule opts for fractional IPV doses at 6 and 14 weeks in the primary series, with a booster at 9 months. However, there are associated risks: cVDPV2 Vulnerability: The extended gap between the second fractional dose and the booster creates a vulnerability to cVDPV2 outbreaks if the virus is imported. Continued Type 3 in OPV: Using type 3 in OPV only carries risks of VAPP without providing protection, as type 3 was globally eradicated in 2012. Persistent iVDPV Risk: The risk of Immunodeficiency-Related Vaccine-Derived Polioviruses (iVDPV) persists until OPV usage is discontinued. “IPV Usage in India: Recommendations and Risks"

11. India should use only monovalent OPV-1, increase IPV coverage in the primary series with one booster (preferably as a combination vaccine), and officially record VAPP cases. This will enable a safe withdrawal of OPV, ensuring all children remain polio-free from both wild and vaccine viruses. In summary, the ongoing polio Endgame needs a clear endpoint. All stakeholders must reassess failed strategies for a certain victory in the shortest time possible. India can lead by establishing its own successful polio Endgame with an improved schedule and sustained IPV coverage.

12. The initial global polio eradication project aimed for 12 years (1988-2000), but its subsequent six Endgames have extended over 23 years with no clear conclusion expected by 2026. However Two key errors occurred: Relying solely on OPV, disregarding its low efficacy in certain Asian and African countries. Neglecting to monitor the risk-benefit balance of OPV over time. Global perspective:

13. 2023 Achievements: Progress made in interrupting endemic wild poliovirus type 1 (WPV1) transmission. Success in preventing outbreaks of variant poliovirus type 2 (cVDPV2). 2024 Focus: Intensified efforts planned for the upcoming year. Continued commitment to diligently work towards the ultimate goal of eradicating polio. GPEI 2023 Achievements and 2024 Focus:

14. Latest Endgame Plan (2022-2026): Aims to interrupt wild poliovirus transmission in Afghanistan and Pakistan. Targets the interruption of transmission of Vaccine-Derived Polioviruses (VDPVs) by 2023. Seeks certification of eradication by 2026. Challenges and Setbacks: WPV-1 polio persists in Afghanistan and Pakistan in 2023, indicating potential failure. In 2022, cVDPV-2 is imported into Israel, UK, and USA. Highlights the emergence of new cVDPV-2 lineages and persistence of existing ones. Global Spread in 2023: Polio due to cVDPV-1 detected in three African countries. Polio due to cVDPV-2 reported in 15 African and two Asian countries. These developments underscore challenges and setbacks in achieving the targets outlined in the latest Endgame plan.