The Hindu: Published on 27th Dec 2024:
Why in News?
Resurgence of polio globally, with both wild poliovirus (WPV) and circulating vaccine-derived poliovirus (cVDPV) being detected in environmental samples and human cases.
Detection of poliovirus in wastewater systems across five European countries (Finland, Germany, Poland, Spain, UK) since September.
Positive environmental samples linked to cVDPV2 strain from Nigeria, highlighting the continued risks of polio despite high vaccination coverage.
Poliovirus:
Subtypes:
WPV has three serotypes:
- Type 1 (WPV1): Most common and responsible for nearly all current polio cases globally.
- Type 2 (WPV2): Declared eradicated globally in 2015.
- Type 3 (WPV3): Declared eradicated globally in 2019.
Vaccine-Derived Poliovirus (VDPV):
A strain of poliovirus that mutates from the weakened virus contained in the Oral Polio Vaccine (OPV).
Types of VDPV:
Circulating Vaccine-Derived Poliovirus (cVDPV):
- Occurs when the weakened vaccine virus spreads in under-immunized communities and regains its virulence.
- cVDPV2: Most common, responsible for recent outbreaks.
Immunodeficiency-Related Vaccine-Derived Poliovirus (iVDPV):
Found in individuals with primary immune deficiencies who cannot clear the vaccine virus.
Ambiguous Vaccine-Derived Poliovirus (aVDPV):
Cases that do not fit into cVDPV or iVDPV categories, often isolated from the environment.
Cause of Emergence:
- OPV use in areas with low vaccination coverage.
- The weakened virus from OPV mutates when it replicates in the intestines and spreads.
Vaccine Poliovirus (Attenuated):
The live, weakened form of poliovirus used in OPV.
Key Features:
- Non-paralytic in vaccinated individuals.
- Capable of spreading in the community, providing indirect immunity to unvaccinated individuals.
- In rare cases, it mutates into vaccine-derived poliovirus (VDPV).
Risk:
While effective in controlling polio, it can contribute to cVDPV cases.
Its use is gradually being phased out in favor of IPV (Inactivated Poliovirus Vaccine).
World Health Organization (WHO) on OPV:
WHO advocates for:
Routine surveillance of wastewater systems to detect and monitor poliovirus.
High levels of vaccination coverage to prevent outbreaks.
Transition from OPV to IPV to eliminate the risk of VDPV.
Current vaccination levels in affected countries range from 85–95%, providing protection against paralysis caused by poliovirus.
Vaccine Controversy:
Debate centers on the use of OPV versus IPV for polio eradication:
OPV:
Live-attenuated vaccine, easy to administer.
Can lead to vaccine-derived polioviruses (VDPV).
Effective for polio control but not eradication.
IPV:
Inactivated vaccine, non-transmissible.
Recommended for eradicating both WPV and cVDPV.
Requires a global, phased withdrawal of OPV to avoid continued cases of vaccine-derived polio.
Respiratory Transmission?
A recent study challenges the dominance of the faecal-oral route in polio transmission:
Suggests that respiratory transmission is the primary mode, akin to measles and diphtheria.
Poliovirus amplification occurs in silently reinfected individuals, facilitating respiratory spread.
Contradicts traditional views that focused on gut virus shedding and contamination.
Conclusion:
- The resurgence of polio highlights the fragility of public health achievements and the need for sustained vigilance.
- A global transition from OPV to IPV is critical to achieving complete eradication of polio.
- Continued research, surveillance, and vaccination campaigns are essential to close immunity gaps and address pockets of undervaccination.
- Policymakers must prioritize a coordinated international strategy to eliminate both WPV and cVDPV, ensuring no child suffers from this preventable disease.
